According to high uniformity requirements of desk lamp lighting, a free curved surface lens is de.signed to perform the secondary light distribution of light emitting diode (LED) light source. Based on the theory ofnon-imaging optics, at the condition of known incident light intensity distribution and required light distribution effect,partial differential equations related to the shape of free curved surface are established. And corresponding numericalvalue algorithm is adopted to obtain the data of the shape of free curved surface. The models of optical lens are builtthrough simulation software Rhinoceros. And optical simulation is performed in Tracepro. The simulation results areobtained to verify the feasibility of the design method.