Using the theory of electromagnetic field and Maxwell equations in medium, we derive the TM mode optical field distribution of resonators with arbitrary cross section. Moreover, taking quadrupolar-shaped microcavity as example, it deduces the eigenvalue equation which contains the propagation constant. Using the software Mathematica, it stimulates the optical field distribution of fundamental mode (m=1) and high-order mode with the different deformation factors, and it is found that the fundamental mode gets the maximum of light emission at φ=45°, 135°, 225°, 315°, it has the feature of “bow-tie” mode. Furthermore, when the deformation factor is 0.1～0.15, the effect is more obviously; however there is not the phenomenon of drawing out the light directionally in the microcavity when m≥2, and it does not form the stable “bow-tie” mode when the deformation factor gets any values. It provides a certain theoretical base for designing and making the quadrupolar-shaped microcavity lasers.