This paper introduces the current development status of high⁃performance cold atomic clocks serving as frequency standards，elaborates on the fundamental principles, performance specifications, applications in metrology and other fields, and development trends of fountain clocks and optical clocks. The analysis focuses on the impact of atomic clock technology advancements on the redefinition of the "second", explores the evolutionary pathways and current status of the redefinition of the "second". It is pointed out that the performance of atomic clocks can be improved by increasing the coherent interaction time, reducing the atomic temperature, and optimizing the uncertainty evaluation strategy. It is proposed that the uncertainty level of atomic clocks can be further improved and their application scope expanded by implementing integrated space⁃time measurements, optimizing the evaluation methods for gravitational redshift, and establishing high⁃level intercontinental remote comparison links.