The invention relates to the computer field, in particular to a password protection method which utilizes a background synchronization method to complete the login process. The method comprises the following steps: an account password is encrypted and saved in a local file via a computer software; the software automatically captures and locks application procedures, client software or web pages, which need to login, at the background of an operation system, then decrypts and sends the account password under a protection state, confirms, submits and simultaneously completes the login process; then the account password information in a memory is cleaned up, thereby protecting each detail in the processes of transporting and submitting the password on a local computer. The invention effectively prevents the harmful procedure from stealing the account password of a user; the user does not need to enter the account password at each time, and the filling and login process is completed automatically by the software; in addition, the invention has the advantages of safety, rapidity and good protection effects on instant messaging, network games, e-business, internet banking, forum blogs, client software and various login applications.