Thank you.

Now I understand this issue. I have another version of GNU Emacs (27.1) 
that works.

This can be closed.

On 2021/7/27 上午2:28, Lars Ingebrigtsen wrote:
> Wensheng Xie <xiewensheng@hotmail.com> writes:
>
>> Debugger entered--Lisp error: (file-error "https://melpa.org/packages/archive-contents" "Bad Request")
>>    signal(file-error ("https://melpa.org/packages/archive-contents" "Bad Request"))
>>    package--download-one-archive(("melpa" . "https://melpa.org/packages/") "archive-contents" nil)
> If I remember correctly, there were some TLS issues in Emacs 26.1 that
> caused these problems.  I'd recommend upgrading to a newer Emacs version
> and see whether that fixes the issue.
>