Abstract: Based on the analysis of the radiation cavity, temperature field uniformity and temperature stability of mediumtemperature blackbody radiation source, the design principle of mediumtemperature blackbody is discussed. With the calculation result of the effective emissivity was taken as the design criterion of cavity, with the obvious effects of the cavity shape and material selection/processing on the improvement of the effective emissivity were considered, and with much count of the heating mode and temperature control algorithm which directly determines the temperature field uniformity and temperature stability was taken, the economical and practical design model of mediumtemperature blackbody radiation source is obtained then. Mediumtemperature blackbody radiation source is developed based on this model. The verified results show that temperature stability reaches to ±0.2℃/h, effective emissivity is 0.99, and temperature field uniformity is 3℃ in the region from cavity bottom to the point at one third of cavity length.