Abstract: A design algorithm that can realize the collimating beam of light was proposed based on free-form surface lens,and an illumination optical system for a single LED source was designed based on the algorithm. The equations of the points on the profile curve about the back surface of the lens were established .By using the iterative method and Matlab programming, a number of discrete points of the free-form profile curve were calculated and fitted to optical entity with the SolidWorks software.Then the optical entity was imported into TracePro software for non-sequential ray tracing.The simulation results show that the optical system can achieve uniform illumination and collimate beam.