A method to design muti-mode fiber collimator by using ZEMAX software is introduced. With the ZEMAX, the theoretical model of the optical system for the muti-mode fiber collimator was built. The zoomy muti-mode fiber collimator was designed and made with artificial optimization. Moreover the simulation results were consistent with the actual results, and confirmed that designing multi-mode fiber collimator is feasible and accurate by ZEMAX. With this model, all kinds of factors on the coupling efficiency and collimation degree of the muti-mode fiber collimator were analyzed.