The chip scale atomic clock is a small, low-power, high-precision time and frequency device. Combining the chip scale atomic clock and the micro inertial measurement unit with the receiver of the global navigation satellite system, a micro positioning navigation and timing unit is formed, which can be widely used in the fields of national economy, military fields and national security. In this paper, the research progress of the chip scale atomic clock at home and aboard is introduced firstly. The difficulties and the key technologies in the preparationdevelopment of the chip scale atomic clock are also expatiated, including micro atomic vapor cell preparation technology, micro electro mechanical system integration technology and chip scale optical frequency comb technology. Finally, the development trend of the chip scale atomic clock is forecastedprospected.