Abstract: Target simulator is essential for test of photoelectricity system. Blackbody radiation source is a key component of the infrared target simulator, and its selection will make a direct impact on the performance of the infrared target simulator. Based on the relation between blackbody detection sensitivity and system detection sensitivity, a formula used to compute the temperature of blackbody radiation source is proposed in this paper. The lowest temperature for blackbody radiation source is calculated by using this method, and it is proved to be correct. This algorithm provides the theoretical basis for selecting blackbody radiation source.