According to the radiation characteristics of LED light sources and lighting requirements of illumination distribution,the energy of LED light source is distributed by using grid method,which corresponds with the small energy blocks in the target plane. We can establish the corresponding relationship between the angle of the light exit from LED light source and the coordinates of point in the target plane. According to the corresponding relationship,calculate the free-form reflector points,and by mechanical modeling software,fit the points to surface entity and import the entity into optical simulation software to carry out the simulation. The results illustrate that through the role of reflector cup on the LED,we can get a uniform rectangular facula in the target surface.