Time-frequency measurement based on a cold atom gas has developed rapidly in the past 20 years and attracted wide attention. A typical example is the optical lattice atomic clock based on many neutral atoms. Using an ultra-stable laser to simultaneously detect the clock transition signals of thousands of cold atoms trapped in the optical lattice, such atomic clocks have achieved the frequency accuracy and the second stability on the order of 10^-18 and 10^-17 respectively, greatly improving the accuracy of time-frequency measurement. In this paper, we review the history, operation principle, performance evaluation and application prospects of optical lattice atomic clocks.