Abstract: A high-emissivity water-bath blackbody cavity was developed in view of the high-precision calibration test of satellite infrared loads. The structural parameters of blackbody cavity were designed based on Gouffe theory, and the process of spraying high emissivity coating was selected after comaring two surface treatment methods. The combination structure with two split circular cones was designed to solve the problems of machining difficulty and coating accumulation in conventional cone tips. The effective emissivity of the developed blackbody cavity was evaluated by theoretical calculation, ray tracing simulation and experimental measurement. The result shows that the effective emissivity of the developed blackbody cavity reaches up to 0.997, which meets the requirement of high-precision calibration test of infrared loads.