The simple working condition method, such as the simple working condition method of C T machine, is to simulate the actual uniform driving condition on the road with professional equipment while keeping the position unchanged, apply corresponding load to the car through instrument setting, simulate the state of the car when it is fully loaded with goods or climbing a hill, and then detect the exhaust emission of the car at this time. The original "double idle speed method" is only used to detect exhaust gas at low idle speed without refueling in neutral and high idle speed with refueling in neutral. But if the car doesn't start, the engine can't burn fully, and it will be in no-load state. The exhaust emission results detected in this way are definitely very different from the actual situation of road driving. Compared with the original double idle speed method, the simple working condition method is more scientific and the detection result is closer to the actual situation. The original idle speed detection method is like a stethoscope; The simple working condition method is more like a C T machine, which can not only detect the real data of exhaust emission when the vehicle is driving, but also diagnose the problems existing in the vehicle and carry out targeted maintenance.