As an important part of the clock circuit, the crystal oscillator is the module with the largest power consumption in the clock circuit, in view of the problem of excessive power consumption of the traditional crystal oscillator, according to the characteristics of the average value of the output voltage signal in the case of starting and stopping the crystal oscillator, a method is proposed to obtain the minimum current required for the oscillator to maintain the oscillation state, which greatly reduces the power consumption of the crystal oscillator circuit. A Pierce oscillation circuit was designed based on the 28 nm CMOS process. The simulation results showed that at a supply voltage of 1.8 V, the circuit can start up quickly within 200 ms, the oscillation frequency is 32.768 kHz, and the oscillator operates at only 270 nA after the output clock signal is stable.