The invention provides a technical scheme, and the scheme is a constant temperature flow type separator which comprises a filter seat assembly, an oil-water separator, a filter element assembly and a filter bowl assembly and is characterized in that a thermodynamic valve assembly is arranged on the filter seat assembly. The thermodynamic valve assembly comprises a valve rod consisting of an uppervalve body and a lower valve body, a reset spring matched with the upper valve body, a thermodynamic connector which is positioned below the lower valve body and fixedly linked with the filter seat assembly and a thermodynamic device which is mounted at the lower end of the thermodynamic connector. The thermodynamic device comprises an outer housing containing thermosensitive wax therein and a push rod. The constant temperature flow type separator adopts the technology of the thermodynamic device with stable performances, thereby fully utilizing residual heat of hot diesel returned by a diesel engine, further greatly reducing the consumption of electrical energy of an electric heater, and not only ensuring that the temperature of the diesel for burning of the diesel engine is matched withthe requirement of the diesel engine, but also thoroughly solving the problem of difficult cold use of the oil water separator for the diesel engine.