A no-common path calibration system was desighned for the Adaptive Optical (AO) system in a 1.23 m ground telescope. To solve some practical problems of no-common path static aberration calibration, the evaluation function for the multi-channel Phase Diversity (PD) processing method was presented for a condition of the defocusinng amount difficult to be measured. Then, a method to use the detected aberration and the modulated deformable mirror to iterate each other for convergence was proposed to make up the effect of nonideal measurement conditions on aberration detection. As compared with two-channel PD processing, the multi-channel PD processing method has stronger tolerance to the forms of target sources and higher accuracy of wavefront solution in theory . The processing method was used to measure the no-common path aberration of the AO system in the 1.23 m telescope. Experimental results demonstrate that the proposed method achieves the higher accuracy of wavefront solution and the aberration has been compensated by using the initial bias of a deformable mirror.Moreover, the whole imaging quality of the optical system is improved effectively.