The operational characteristics of Z-shaped orthogonal porro-prism resonator are theoretical analyzed using Jones matrix optics.The relationship between azimuth angle of waveplate and polarizer transmission,effective reflectivity in feedback arm,coupling reflectivity in output arm,waveplate number which compensates the phase shift introduced by Porro prism is studied.The analysis is done with several different refractive indices of Porro prism.Using rate equation and fourth-order Runge-Kutta method,the influence of output arm′s coupling reflectivity on the output energy and pulse width of the Q-switched laser is theoretically analyzed.