For most of the auto-focus function′s problems of focus curve losing desirable characteristics ,falling into local minum value and even losing single peaks,which are caused by changes in contrast,Zernike orthogonal moments was introduced and the focus curves were analyzed.A new auto-focusing algorithm was presented which based on Zernike orthogonal moments and the algorithm′s formula was defined.Compared with the focusing effect of several commen auto-focus funtions under different contrast,the algorithm can adapt to different contrast under the focusing process by adjusting the weighting coefficients to change the formula.The experiment compared the algorithm focus curves′ difference between completely symmetric objects and non-symmetric objects,proved that the algorithm is more effective for the completely symmetric objects such as the round or spherical objects.