Objective To establish a new model of cardiac rhythm. Methods Two Hodgkin-Huxley equations are used to simulate the potential of SA node and AV node, and to describe the regular pattern of cardiac rhythm. Results It has been found out that the results of the model analysis are similar as the actual situation on the influence of external stimulus and ions to the cardiac rhythem.Conclusion This mathematics model can describe the change of cardiac rhythm. The structure of the model is clear enough and the data have some physiological meaning.