Wave-front fitting capability analysis is an important part of adaptive secondary mirror′s design. Fitting capability simulation of 1.8 m telescope′s adaptive secondary mirror based on finite element analysis (FEA) influence function is presented. Analysis results show that the 73-element adaptive secondary mirrors can fit the 44-term Zernike polynomials with lower fitting errors. Mean fitting errors of 10000 frames of Kolmogorov phase screens is about 0.0541. Invalidated actuators near pupil edge induce fitting capability to reduce fearfully. Since the 73-element adaptive secondary mirror has better fitting ability with an actuator broken, the scheme has been chosen as 1.8 m telescope′s adaptive secondary mirror.