The transfer equation of the principal ray is used to study the relationship between the compression ratio of the field angle and the optical parameters of the pre-group optics of fisheye lens, and then the design parameters of the pre-group optics of fisheye lens are determined according to the requirement of compression ratio and lens dimension. Since the pre-group optics has the imaging performance of a plane-symmetric optical system, the aberration theory of plane-symmetric optical systems is applied to calculate its wave aberration. The focal power of every component and the gap between them can be solved from the wave aberration balance equations of pre- and back-group optics of fisheye lens. The solution is used as constraints, and Zemax is used to obtain a simple initial design of back-group optics consisting of three lenses. The lens complication and optimization is then performed according to the simple system. A fisheye lens is obtained, which satisfies the reguirement of bigger field of view and aperture. The study shows that the method discussed in the paper provides an approach to determine the initial structure design of fisheye lens and enables the designers not to rely heavily on experience and patents.