An automatic testing system is developed to test directional radiometric characteristics of large aperture integrating spheres quickly and precisely. The testing system is made up of a scan unit,a trap detector and a control unit. The control unit controls the scan unit fixed with the trap detector to displace according to the set position, then controls the data collector to collect,display and save the data.The system shows its scan ranges of plan uniformity and the directional characteristic are 1 m×1 m and ±60°,respectively. The system is used to test a large aperture integrating sphere with a diameter of 2.5 m,which is automatic and characterized by high precision and efficiency. Obtained results indicate that the plan uniformity is 0.19%, and the maximum offset of Lambert characteristic is 1.03% at ±45°.Currently,the system has been successfully applied to the test of large aperture integrating spheres for many times,and satisfied results are obtained.