In order to improve the heat dissipation performance of light emitting diode (LED), based on the principle of the chimney effect, a special cooling radiator with straight chimney structure for LED is designed. The three-dimensional model is built by Solidworks software, and the model is simulated by its plug-in called Flow Simulation. The effects of various heights, vent shapes and sizes on the heat dissipation of chimney effect are studied. Studies show that chimney effect effectively improves the convection cooling performance of the radiator. When the height of chimney is 50 mm and the equivalent diameter of trapezoidal vent is 8 mm, the highest temperature of the LED is 61.6 ℃， which is 6.54 ℃ lower than the original model. Compared with the traditional radiator, the highest temperature of LED reduces 8.89 ℃. Through experiments, the average error between the actual temperature of the 4 monitoring points and the simulated temperature is 4.0%, and the average error is in the allowable range. It confirms the correctness of the simulation steps. In conclusion, the designed radiator can better satisfy the working requirements under the nature convection conditions.