Roots fan is composed of five parts: shell, wall panel, impeller, fuel tank and muffler. Because of the three-blade rotor structure and the reasonable structure of the inlet and outlet in the shell, the fan has low vibration and low noise. The impeller and shaft are an integral structure and the impeller has no wear, the fan performance is durable and unchanged, and it can run continuously for a long time. The fan has large volume utilization rate, high volume efficiency, compact structure and flexible installation mode.