Abstract: The cold atom clock based on Ramsey interrogation has been proved to have high stability and accuracy. After nearly 30 years of development, the technology maturity and the reliability of the cold atom clocks are improved, and it has been gradually applied in portable time-frequency systems. The miniaturization of cold atom clock thus becomes a research hotspot in this field. The working principle and operation process of cold atom microwave clock based on Ramsey interrogation are expounded. The key technologies and the research status of miniaturization of cold atom clock are analyzed and reviewed, respectively. It is shown that the in-situ interrogation technology based on the preparation of cold atoms in the cavity is an effective way to realize the miniaturization of cold atom clock, which will make the cold atom clock has the advantages of high performance, high reliability and high integration.