diff --git a/src/sm4_cfb.c b/src/sm4_cfb.c
index e086b3b2..a169eaea 100644
--- a/src/sm4_cfb.c
+++ b/src/sm4_cfb.c
@@ -13,24 +13,25 @@
 #include <gmssl/error.h>
 
 
+// sm4_cfb_encrypt iv type is not compatible with sm4_cbc_encrypt, carefull if inlen % sbytes != 0
 void sm4_cfb_encrypt(const SM4_KEY *key, size_t sbytes, uint8_t iv[16],
 	const uint8_t *in, size_t inlen, uint8_t *out)
 {
 	uint8_t block[16];
 	size_t len, i;
 
-	// assert(1 <= sbytes && sbytes <= 16);
-
 	while (inlen) {
 		len = inlen < sbytes ? inlen : sbytes;
+
 		sm4_encrypt(key, iv, block);
+
 		gmssl_memxor(out, in, block, len);
 
 		// iv = (iv << sbytes) | out
 		for (i = 0; i < 16 - sbytes; i++) {
 			iv[i] = iv[sbytes + i];
 		}
-		memcpy(iv + i, out, len);
+		memcpy(iv + 16 - sbytes, out, len);
 
 		in += len;
 		out += len;
@@ -44,18 +45,19 @@ void sm4_cfb_decrypt(const SM4_KEY *key, size_t sbytes, uint8_t iv[16],
 	uint8_t block[16];
 	size_t len, i;
 
-	// assert(1 <= sbytes && sbytes <= 16);
-
 	while (inlen) {
 		len = inlen < sbytes ? inlen : sbytes;
+
 		sm4_encrypt(key, iv, block);
-		gmssl_memxor(out, in, block, len);
 
 		// iv = (iv << sbytes) | in
 		for (i = 0; i < 16 - sbytes; i++) {
 			iv[i] = iv[sbytes + i];
 		}
-		memcpy(iv + i, in, len);
+		memcpy(iv + 16 - sbytes, in, len);
+
+		// NOTE: must update before output, in might be changed if in == out
+		gmssl_memxor(out, in, block, len);
 
 		in += len;
 		out += len;
@@ -191,6 +193,8 @@ int sm4_cfb_decrypt_update(SM4_CFB_CTX *ctx,
 	}
 	*outlen = 0;
 	if (ctx->block_nbytes) {
+		error_print();
+
 		left = ctx->sbytes - ctx->block_nbytes;
 		if (inlen < left) {
 			memcpy(ctx->block + ctx->block_nbytes, in, inlen);
diff --git a/src/sm4_ofb.c b/src/sm4_ofb.c
index cf82e236..2dc03f37 100644
--- a/src/sm4_ofb.c
+++ b/src/sm4_ofb.c
@@ -13,6 +13,7 @@
 #include <gmssl/error.h>
 
 
+// sm4_ofb_encrypt iv type is not compatible with sm4_cbc_encrypt, careful if inlen % 16 != 0
 void sm4_ofb_encrypt(const SM4_KEY *key, uint8_t iv[16], const uint8_t *in, size_t inlen, uint8_t *out)
 {
 	size_t len;
diff --git a/tools/sm4_cfb.c b/tools/sm4_cfb.c
index a8e18212..b1077ec3 100755
--- a/tools/sm4_cfb.c
+++ b/tools/sm4_cfb.c
@@ -18,12 +18,13 @@
 #include <gmssl/error.h>
 
 
-static const char *usage = "{-encrypt|-decrypt} -key hex -iv hex [-in file] [-out file]";
+static const char *usage = "{-encrypt|-decrypt} -sbytes num -key hex -iv hex [-in file] [-out file]";
 
 static const char *options =
 "\n"
 "Options\n"
 "\n"
+"    -sbytes num         Parameter sbytes of CFB mode, should be 1, 8 or 16, 16 by default\n"
 "    -encrypt            Encrypt\n"
 "    -decrypt            Decrypt\n"
 "    -key hex            Symmetric key in HEX format\n"
@@ -36,8 +37,14 @@ static const char *options =
 "  $ TEXT=`gmssl rand -outlen 20 -hex`\n"
 "  $ KEY=`gmssl rand -outlen 16 -hex`\n"
 "  $ IV=`gmssl rand -outlen 16 -hex`\n"
-"  $ echo -n $TEXT | gmssl sm4_cfb -encrypt -key $KEY -iv $IV -out sm4_cfb_ciphertext.bin\n"
-"  $ gmssl sm4_cfb -decrypt -key $KEY -iv $IV -in sm4_cfb_ciphertext.bin\n"
+"  $ echo -n $TEXT | gmssl sm4_cfb -encrypt -key $KEY -iv $IV -out sm4_cfb128_ciphertext.bin\n"
+"  $ gmssl sm4_cfb -decrypt -key $KEY -iv $IV -in sm4_cfb128_ciphertext.bin\n"
+"\n"
+"  $ echo -n $TEXT | gmssl sm4_cfb -sbytes 1 -encrypt -key $KEY -iv $IV -out sm4_cfb8_ciphertext.bin\n"
+"  $ gmssl sm4_cfb -sbytes 1 -decrypt -key $KEY -iv $IV -in sm4_cfb8_ciphertext.bin\n"
+"\n"
+"  $ echo -n $TEXT | gmssl sm4_cfb -sbytes 8 -encrypt -key $KEY -iv $IV -out sm4_cfb64_ciphertext.bin\n"
+"  $ gmssl sm4_cfb -sbytes 8 -decrypt -key $KEY -iv $IV -in sm4_cfb64_ciphertext.bin\n"
 "\n";
 
 int sm4_cfb_main(int argc, char **argv)
@@ -45,6 +52,7 @@ int sm4_cfb_main(int argc, char **argv)
 	int ret = 1;
 	char *prog = argv[0];
 	int enc = -1;
+	int sbytes = SM4_CFB_128;
 	char *keyhex = NULL;
 	char *ivhex = NULL;
 	char *infile = NULL;
@@ -86,6 +94,14 @@ int sm4_cfb_main(int argc, char **argv)
 				goto end;
 			}
 			enc = 0;
+		} else if (!strcmp(*argv, "-sbytes")) {
+			if (--argc < 1) goto bad;
+			sbytes = atoi(*(++argv));
+			if (sbytes != SM4_CFB_8 && sbytes != SM4_CFB_64 && sbytes != SM4_CFB_128) {
+				fprintf(stderr, "%s: value of `-sbytes` should be %d, %d or %d\n", prog,
+					SM4_CFB_8, SM4_CFB_64, SM4_CFB_128);
+				goto end;
+			}
 		} else if (!strcmp(*argv, "-key")) {
 			if (--argc < 1) goto bad;
 			keyhex = *(++argv);
@@ -148,12 +164,12 @@ bad:
 	}
 
 	if (enc) {
-		if (sm4_cfb_encrypt_init(&ctx, 16, key, iv) != 1) {
+		if (sm4_cfb_encrypt_init(&ctx, sbytes, key, iv) != 1) {
 			error_print();
 			goto end;
 		}
 	} else {
-		if (sm4_cfb_decrypt_init(&ctx, 16, key, iv) != 1) {
+		if (sm4_cfb_decrypt_init(&ctx, sbytes, key, iv) != 1) {
 			error_print();
 			goto end;
 		}