Based on a reversed blade angle slots casing treatment with good stability expansion performance, three schemes of reversed blade angle slots-circumferential groove coupling casing treatment are obtained by adding a circumferential groove at different axial positions of the reversed blade angle slots, and are applied to the FBCDZ-No20 coal mine contra-rotating main fan. The influence of the reversed blade angle slots casing treatment and the three schemes of slots-groove coupling casing treatment on the stability expansion performance of the fan has been compared and analyzed numerically. The results show that the reversed blade angle slots casing treatment effectively improves the stability margin of the contra-rotating fan. The implementation of the three schemes of slots-groove coupling casing treatment further improves the sta-bility margin of the fan, but they also result in varying degrees of reduction in peak efficiency. Among them, when the circumferential groove is located at the front end of the reversed blade angle slots, the stability expansion effect is the best, but the efficiency loss is also the largest. As the circumferential groove moves towards the trailing end of the slots, the stability expansion capacity gradually weakens. After a slots-groove coupling casing treatment is implemented, the driving force of the blade tip leakage flow increases due to the considerable change of the pressure difference between the suction surface and pressure surface of the front stage blade. In addition, with the suction and injection effects of the airflow in the blade tip channel of the front stage, the low-speed air flow in the blade tip channel is blown away, reducing flow blockage, increasing the axial velocity of the blade tip leakage flow, improving the flow situation in the blade tip region, delaying the occurrence of stall, and thereby improving the stability margin of the fan. ?However, the flow losses generated by the airflow inside the slots-groove coupling casing treatment, as well as the flow losses caused by the mixing between the jet generated by the casing treatment and the airflow in the blade tip channel, all lead to a decrease in the peak efficiency of the fan.