Can't remember the key private key passphrase

My version is 5.5.6, I use private key for logging in, but it can't remember the key passphrase.
I have to key-in the passphrase every time I login in.
I saved the session and the also the password.

Passphrase and password are two different things.
WinSCP does not support remembering a passphrase. It does not make sense.
See How can I connect without entering private key passphrase each time?