In order to improve the luminous energy rate of dipped headlight in the LED projection headlamp systemcommonly used in vehicles,the relationships between the lighting distribution of LED dipped headlight and the lightsource energy as well as the freeform lens parameters were investigated based on the theory of non- imaging optics,and a design method of LED freeform lens for vehicle dipped headlight was proposed based on the infinitesimalenergy mapping.Then,in order to verify the feasibility of this design method,a LED lens was designed with thesoftware Rhino,and an illumination system of LED dipped headlight was constructed with the software Tracepro.Simulated results indicate that the designed lens not only provides illumination patterns matching the dipped head-lamp regulation but also possesses a luminous energy rate increment of 23. 5%,as compared with the traditionalLED projection headlamp system.