The optical design of a short focus and ultra-wide field of view (FOV) lens used for monitoring is discussed. The optical system uses inverted telephoto optical structure. The equidistant projection imaging mode is adopted according to the design requirements. The Zemax software is adopted to optimize and design the system. The marginal FOV illumination and off axis aberration are solved. The structure features of the lens are discussed and the aberration curves and medulation transfer function (MTF) curves are showed. The lens has a structure of 7 groups and 10 pieces. The marginal FOV and relative aperture of the final design is up to 175° and 1/1.8 respectively, and inverted telephoto ratio is 2.4. Using 1/3 ″CCD imaging device, full FOV MTF value reached 0.5 at 100 lp/mm. Optical system has compact structure, excellent image quality.