The Lug-down emission test system is suitable for the emission test of diesel vehicles with compression combustion engine. The system consists of chassis dynamometer, opaque smoke meter, cooling device, driver assistant, safety inhibiting device, inertia simulator, engine tachometer, environment and computer control system. Through power scanning, the system detects the measured maximum wheel-edge power and the corresponding engine speed and drum linear speed (VelMaxHP) of dynamometer, so as to test the three smoke values of the vehicle at three points of VelMaxHP, 90%VelMaxHP and 80%VelMaxHP, and judge whether the emission of the vehicle is qualified or not according to the standard limit value.