The geolocation performance of tri-satellite system based on time difference of arrival (TDOA) is significantly affected by the constellation configuration. In this paper, an angle condition number based method is proposed for constellation configuration analysis. First, the coefficient matrix of constellation configuration is derived by geolocation error analysis. Second, the angle condition number is adopted to measure the ill-condition of the coefficient matrix. Based on the measurement, the influence of constellation configuration on geolocation is deeply analyzed. The effectiveness of angle condition number on constellation configuration analysis is verified by simulations.