The utility model provides a diluting mixing system which relates to the technical field of environment monitoring equipment. The system comprises a zero gas generator, a mass flow rate controller, a heating pipe line, a mixing chamber and temperature and humidity sensors so as to simulate the mixing, diluting and cooling process of tail gas of a moving source when being discharged to the atmosphere and a forming process of secondary pollutants. The system provided by the utility model which can be widely applied to vehicle-mounted tests and rack experiments of various moving sources.