In recent years, all kinds of deformed micronano cavities with high quality factor and directional output have been extensively studied, since they can be widely used for the realization of the extremely low threshold lasers in optoelectronic integrated. In this paper, we calculate the variation of mode pattern, quality factor and far field characteristics as the cavity evaluates from circular to ellipse with the changes of the short half axis changes using the boundary element method. The simulation results show that the larger the ellipse curvature is, the lower the mode quality factor, and the mode field transforms from the whispering gallery mode to the regular Fabryperot cavity mode. However, during the deformation transformation, the mode coupling effect leads to the abnormal change of the mode quality factor, and the modulation of the far field. This mechanism provides a new design idea for the laser with both directional output and high Q value.