With the digital logic calibration circuit module and current mirror array adjusting and controlling the input current and charge and discharge current of the ring oscillator, this paper designs a high precision clock generating circuit with a frequency of 2MHz, which has the characteristics of high stability, fast calibration and simple circuit structure. The circuit is simulated with smic0.18um technology. The results show that the error of the clock frequency is within 1%, and the maximum time is less than 400μs.