I finally found the problem. My anti-virus software(360安全卫士) blocks emacs to emulate lwindow key. When emacs is trusted by anti-virus software, the problem is solved.
Thank you for all your help.
------------------ 原始邮件 ------------------
发件人: "Albert"<georgealbert@qq.com>;
发送时间: 2019年9月26日(星期四) 晚上9:40
收件人: "Eli Zaretskii"<eliz@gnu.org>;"Juanma Barranquero"<lekktu@gmail.com>;
抄送: "37495"<37495@debbugs.gnu.org>;
主题: 回复： bug#37495: 回复： bug#37495: 27.0.50; lwindow doesn't pass to system
Emacs 26.2/26.3/27.0.50 are downloaded from gnu website(http://ftp.gnu.org/gnu/emacs/windows/emacs-26/ and http://alpha.gnu.org/gnu/emacs/pretest/windows/emacs-27/).
I tried to comment code in w32fns.c to bypass lwindow to system, but failed without luck.
------------------ 原始邮件 ------------------
发件人: "Eli Zaretskii"<eliz@gnu.org>;
发送时间: 2019年9月26日(星期四) 晚上8:17
收件人: "Juanma Barranquero"<lekktu@gmail.com>;
抄送: "Albert"<georgealbert@qq.com>;"37495"<37495@debbugs.gnu.org>;
主题: Re: bug#37495: 回复： bug#37495: 27.0.50; lwindow doesn't pass to system
> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Thu, 26 Sep 2019 13:45:03 +0200
> Cc: Eli Zaretskii <eliz@gnu.org>, 37495 <37495@debbugs.gnu.org>
>
> Why it didn't happen with 26.2, I have no idea.
Maybe Emacs 26.2 was downloaded from a different site, or it was a
different build?