A Coherent Population Trapping(CPT) atomic clock servo control circuit is designed based on the CPT phenomenon of 85Rb. Taking MSP430 chip as a platform, combining with the physical device made up of Vecsel laser, photoelectric detector, and small 85Rb vapor cell, a miniature atomic clock with the high-performance, high stability, low power consumption and small size is implemented. The volume is 31 cm3 and the power consumption is 660 mW. The frequency stability of 10 MHz measured is 2×10-10/s, 4×10-11/1 000 s. Full-hyperfine-splitting frequency modulation is used to improve the frequency stability.