Already tried this, here are my steps
1.Interrupt u-boot
2.tftpboot initramfs.bin
3.bootm
4.Upload sysupgrade.bin to winscp for upgrade.
5.sysupgrade -n /tmp/sysupgrade.bin
I just saw an incompatibility report in the repository. Maybe I already understand the situation。
https://github.com/openwrt/openwrt/commit/fbcda3616e2c18b533a552fad9b724a636bcae5e