Mercury ion microwave clock is an ideal candidate for the next generation spaceborne atomic clock and ground?based timekeeping atomic clock. This paper briefly introduces the operation procedure and research status of mercury ion microwave clock, especially the latest research progress made by our group in the key technologies, including the ion trapping, buffer gas cooling, microwave synthesizer and mercury discharge lamp. On this basis, a miniaturized prototype of mercury ion clock has been built using these technologies and demonstrated frequency stability of 2.3 × 10^-15/10⁵ s. An extended linear ion trap mercury ion clock is also under development. The ions can be trapped and shuttled back and forth efficiently in the extended ion trap. Frequency stability of 3.45 × 10^-13/τ^1/2(τ = 10～10 000 s) has been measured in preliminary close?loop operating. All these works lay an important foundation for the further application of mercury ion microwave clock technology.