The length of Fragment header in IPv6 From RFC2460 :< the length of the fragment header seems to be fixed 8 bytes. But when I test with Scapy with the default fragment header, from sniffer I can see the fragment header is for one byte? That is the data generated by Scapy seems not consistent with the specification? I'm not sure in the real world, what will this header will be designed?

You question is confusing. The fragmentation header is 8 bytes. You say the observed payload is 1 byte. The payload is not the header, and the size of the header has nothing to do with the size of the payload.

**Edit based on your comment and correction of the the question:**

The fragmentation header is 8 bytes. You may be reading the results incorrectly, or it is possible that the application you are using doesn't correctly understand what it is seeing.