Casing treatment (CT) has proven to be an effective way to enhance stability, and has a very important role in enhancing the stability of the compressor. Researchers have made great achievements and progress in the study of single-type CT structure, but less research on combined-type CT structure. In this paper, the isolated rotor of a high-load axial-flow compressor is taken as the research object, and the numerical simulation method is used to study the enhancing stability mechanism of the combined-type casing treatment (ASCT) by combining the axial slot casing treatment (ASC) and the self-circulating casing treatment (SCT). The study found that the reasonable choice of the ASCT scheme can make the enhancing stability effect of the ASCT higher than that of the single-type CT structure scheme. Through detailed quantitative analysis of the rotor’s internal flow field, it was found that ASC and SCT can suction the airflow downstream of the rotor passage, and then spray it into the main flow from the upstream of the rotor passage, and the blade tip blockage is reduced, the flow capacity of the blade tip passage is improved, and the rotor stability is enhanced by suppressing tip clearance leakage flow. The ASCT has both the spraying effect of the ASC and the SCT, and has the best improvement effect on the flow blockage zone in the rotor passage, and the obtained enhancing stability effect is also best. In addition, the circulation and re-injection of the airflow after CT has aggravated the flow blending loss in the blade tip zone, which has reduced the rotor efficiency. The ASCT has both the characteristics of the effect of the ASC and the SCT on the rotor efficiency, resulting in a large reduction in the rotor efficiency after using the ASCT.