Roots blower

The invention relates to a roots blower which comprises a machine shell, an impeller, an air inlet, an air outlet and an involute type buffer air groove. The involute type buffer air groove is formed in one side of the air outlet inside the machine shell, the two sides of the involute type buffer air groove are increased from small to big and deepened from shallow to deep, and the big end of the involute type buffer air groove is located in one edge of the air outlet. The roots blower is characterized in that when the impeller of the blower is close to the air outlet, due to the fact that the sectional area of the involute type buffer air groove is increased from small to large step by step, the communication flow of a pressure cavity and the air outlet is increased from small to big, the pressure in the air outlet and the pressure in the cavity are balanced gradually so that the pressure in the pressure cavity can be prevented from being suddenly lowered, high-pressure air in an exhaust port flows back and impacts to generate pressure fluctuation, and therefore vibration and noise are reduced.