Abstract: The reason,the condition and the degree of modal coupling and aliasing in wavefront reconstruction are pointed by simulating the measure and Zernike modal wavefront reconstruction course of 19-element Hartmann-Shack wavefront sensor.Considering the maximum distinguished modal and stability of calculation,the principle of selecting optimal value of Zernike reconstruction is found.The analysis of the accuracy of reconstruction shows that modal coupling is main error for 19-element Hartmann-Shack sensor's wavefront reconstruction.The condition and the accuracy of the wavefront measured with 19element Hartmann-Shack wavefront sensor is received.