what are you SSH'ing from? Putty? Another Linux server?
You can:
ssh user@1.2.3.4
ssh -v user@1.2.3.4
ssh -vv user@1.2.3.4
ssh -vvv user@1.2.3.4
Each will show progressively more verbose details about what's happening and why you might be getting refused. SM7 does use newer ciphers for SSH and it tries to be secure and drops older ciphers, so older versions of putty won't work.
For example, if I go in my AAM/MSS at 6.3 and try SSH'ing to SM7, I get this:
admin@mss> ssh user@1.2.3.4
no matching mac found: client hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 server hmac-sha2-512,hmac-sha2-256