The uniform light sources are widely used in optic imaging fields ,as well as the development and calibration of remote sensing instruments. For irradiation uniformity, an integrating sphere structure with an annular baffle was proposed. Based on Monte Carlo method, the structure was analyzed and optimized by changing the parameters including light source type, baffle position, slotting size and number of light sources. Results show that the average irradiation uniformity of the Lambert light source is 2.32% higher than the collimated light source. When the baffle is located close to the edge of integrating sphere, the irradiation uniformity is slightly lower than other positions. Considering the radiation energy and illumination uniformity, the open ratio is suggested to be limited in the range of 30%~35%. The radiation power has a linear relationship with the number of light sources,and the nonuniformity fluctuates with the number of light sources from 2.46% to 3.38%. The optimized annular baffle structure is proposed as irradiated uniform light source in practical application scenario.