Abstract: In order to study the mode distribution in a laser resonator, a circular mirror resonator was analyzed based on finite element matrix and the feasibility and effectiveness of this method was verified. On the basis of the study, the rational division of the cavity mirror was studied. After fitting the relationship between the relative error and the fine extent of division elements, the reasonable number of elements was obtained. The results conformed with the actual calculation and analysis well. The results show that this method makes the mode analysis of a laser resonator more accurately and conveniently.