In the current stable release of WinSCP, it seems that using SshHostKeyFingerprint is mandatory and there are no ways to connect to SFTP server without that in SessionOptions. I can see that the ability to bypass is added to the beta (5.2) but I was wondering whether or not it's possible to connect without this fingerprint.
First, make sure you understand that you give-up any security, when you try to bypass SSH host key check. You effectively lose a protection against man-in-the-middle attacks.
Anyway, you can use use SessionOptions.GiveUpSecurityAndAcceptAnySshHostKey.
It's NOT recommended though. You should always set SessionOptions.SshHostKeyFingerprint.
Learn how to determine SSH host key fingerprint.
来源：https://stackoverflow.com/questions/17938825/winscp-net-library-connect-to-sftp-server-without-specifying-ssh-host-key-fing