This research is analyzed heat transfer shell of LED by Moldex 3D software and to decrease the weight of LED shell using plastic material. Using Mg alloy can enhance heat transfer and solve the exhaust heat form LED and maintain the life of LED. The other purpose is to decrease the weight of LED shell and satisfy the costumer request. Therefore, we use Moldex3D to analyze and get the result of wrapage to meet the fine tolerance to improve fitness of LED.