The proportion of LED in the lighting area gradually increased. But its high price, the low luminous efficiency, reliability problems restricted its global application. Therefore, for reliability problems, design a thermal structure of 19.2W multi-chip on board aluminum plate LED. Enhance the reliability mainly by settle a piece of silicon between the aluminum plate and the chips. Analyze by finite element method and use the ANSYS simulation software, the simulation for the thermal field is performed. Identify the optimal combination of structural parameters by using the orthogonal experimental method. The maximum steady-state temperature is less than 53.69 °C. Analyze the thermal-structure coupling simulation of the optimization of the thermal structure and reach the maximum thermal stress of 144MPa. So we can say that heat stress in terms of the design is safe and reliable. Eventually arrive at a more ideal LED aluminum plate thermal structure.