A password input system and a method inputting a password are provided. The password input system includes a signal receiving unit, a processing unit and a storage device. The signal receiving unit receives input signals comprising key-pressing signals and key-releasing signals respectively corresponding to the key-pressing signals and each key-pressing signal corresponds to an alphanumeric symbol. The processing unit, according to a predetermined key-releasing rule, sequentially groups the alphanumeric symbols corresponding to the key-pressing signals into groups. Each group is regarded as a password element and the password elements together form a multi-key input password set. The storage device stores the multi-key input password set.