Any a field ray, using its transfer equations, is traced reversely from the aperture stop of a fisheye lens to determine its initial position, i.e., the pupil spherical aberration. Then tracing the field ray in its forward direction, a relation curve between the field angle of object and image space can be obtained; a polynomial expression is used to fit the relation curve. By the inversion operation to the polynomial expression, the distribution of object without distortion can be rectified from the distorted image to realize the purpose of eliminating the distortion of fisheye lens. Finally, we make numerical calculations of the pupil spherical aberration and image distortion to a 160°-fisheye lens, and rectify the distortion of object. The calculation results show that, the relative error of the pupil spherical aberration from the exact value is less than 1%, and the relative error of radial height of the rectified object distribution is less than 0.25%. The research shows that the method is feasible for the calculation of the field-dependent aberrations of fisheye lens.