A high-stability shift circuit using amorphous silicon thin film transistors, which utilizes two out-of-phase pulses to control the operating mechanism and the bias-relations among transistors in the shift circuit. This makes the transistors under the driving conditions of positive/negative-alternating biases so as to restrain the voltage shift of the transistors such that the threshold voltage will not excessively increase along with the increasing operating time. This can not only increase the lifetime of the amorphous silicon thin film transistors but also extend the operating time of the shift circuit.