The invention provides a casing treatment device for reducing stalling and surging of an air compressor. The casing treatment device comprises a casing and a space ring. The casing comprises an air inlet shell and an impeller. An annular flow division groove is fixedly formed in the position, opposite to the side wall of the air inlet shell, of the front side of the front impeller edge of the impeller. The annular flow division groove is provided with an opening facing the interior of the air inlet shell. The space ring is in a barrel shape and is fixed to the inner side wall of the air inlet shell and located at the opening of the annular flow division groove. According to the casing treatment device for reducing stalling and surging of the air compressor, the space ring is adopted for automatically separating main flow and casing treatment inner flow, the casing treatment inner flow is guided to the impeller tip direction and the axial inflow direction, and therefore the mixing loss of the main flow and the casing treatment inner flow is reduced, and backflow or counterflow generated by the impeller tip area is suppressed more effectively; and therefore stalling and surging are reduced, and under the condition of large flow, the influence of the groove on the main flow is smaller than that in a conventional method, and the influence of the groove on efficiency can be reduced.