Automatic voice query system for bank by phone was a hi-tech product based on computer technology, electronic communication technology and speech synthesis technology. The hardware design of this system adopted modularization design scheme, which centered on SCM AT89C51, and controlled the phone transceiver chip MT8870 and voice chip ISD4004, realizing voice query for bank account by phone remote control. This paper mainly analyzed and designed several circuits such as ringing detection circuit, on-hook and off-hook control circuit, amplified-filter circuit, receiving circuit, voice circuit and the connection circuit between PC and SCM; it finally gave the realization process of the system’s software.