您很接近，但是您传递给SecureStringToBSTR的参数必须为SecureString.您似乎正在传递ConvertFrom-SecureString的结果，该结果是加密的标准字符串.因此，在传递给SecureStringToBSTR之前，先对此调用ConvertTo-SecureString.

You are close, but the parameter you pass to SecureStringToBSTR must be a SecureString. You appear to be passing the result of ConvertFrom-SecureString, which is an encrypted standard string. So call ConvertTo-SecureString on this before passing to SecureStringToBSTR.

$SecurePassword = ConvertTo-SecureString $PlainPassword -AsPlainText -Force
$BSTR = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($SecurePassword)
$UnsecurePassword = [System.Runtime.InteropServices.Marshal]::PtrToStringAuto($BSTR)