The hardware modules of electronic password lock were designed in the paper. The single chip microcomputer AT89S51 was chose as the main control chip to control the operation of the whole system. The 4×4 matrix keyboard was devised and the unlocking circuit was made up of the driving circuit and unlocking part. The alarm circuit was composed of a piezoelectric buzzer and its peripheral circuit. The serial electrically erasable memory chip AT24C02 of ATMEL firm was chose as the memory cell for losing electricity. The power supply circuit including of the commercial power supply circuit, power failure detecting and electronic switching circuit and the battery charging circuit was designed. The module functions of the whole system were combined and the hardware circuits of the electronic password lock were designed successfully.