Circadian rhythms are endogenous oscillations characterized by a period of about 24h. The abundance of genetic information and the complexity of the molecular circuitry make circadian clocks a system of choice for theoretical studies. Mathematical model can help us understand the molecular regulatory mechanisms that underlie these circadian oscillations and account for their dynamic properties. By numerical simulations, mathematical models can highlight the role of key parameters and can be used to predict the behavior of the system in conditions not yet tested by experiments. Mathematical models can also be used to provide possible explanations to unintuitive observations or to unravel the design principles of the circadian molecular oscillator. In this paper, we summarized the mathematical models used in circadian clock. The building and analysis of mathematical model,as well as its advantages and limitations, were highlighted. All of these will provide scientific basis for further studying on circadian clock, and even for derstanding the functions of mathematical model in life system．