In order to inspect defects of projection objective using microscope m ore effectively,according to the relationship between the ray incidence angle an d coefficient of wavefront coding phase mask,a wavefront coding phase mask is designed,which can be applied to 5X,10X,20X objectives simultaneou sly.Optimization results show that the modulation transfer functions (MTFs) of t he optical systems with different power objectives preserve fine value in a large defocus range,and can multiply the depths of field of 5X,10X,20X obje ctives by 3to 10times without resolution reduct ion.Finally,the abilities of defocus imaging with and without the wavefront coding phase mask are compared.These resu lts show that the optimized wavefront coding phase mask is flexible and practical in the inspection defects of projection objective using microscope.