Hi @jinglin
Glad you discovered how to adjust the datatype, and thanks for posting back the solution!
I’m going to post some FAQs for anyone else who find this topic with a search.
Galaxy will try to detect the exact datatype but sometimes the overlap in content between many file types makes that difficult. In those cases, a more generic type is the fall back. And while a wrong “guess” can also indicate a format issue .. that isn’t always true of course! Directly reassigning is the solution. 