In the traditional printing, curing light source always uses high pressure mercury lamp, metal halide lamp and so on. The traditional light source of ultraviolet curing technology has been matured. But because of the light source itself and the limitations of the optical system, the linear light radiation intensity of illumination is low. And the uniformity of the light field is not high enough. This paper provides a design of freeform surface which makes the emergent light of ultraviolet-LED becoming a linear light source effectively. The SolidWorks software is used to design initial structure of the lens. And then the structure is imported into LightTools software to simulate the light. The light is optimized by establishing the objective function and changing the parameters, so that the emergent light can present high brightness and high linear light evenness.