The premature scrapping of aviation 9310 steel gear shafts due to wear during their service life greatly increases the cost of aviation equipment. Surface treatment of gear shafts is an important method to extend the life of aviation equipment. At present, the influence mechanism of surface treatment methods on the fatigue of 9310 steel gear shafts is not clear. So it is necessary to conduct a research on the influence of different surface treatment methods on the bending fatigue performance of 9310 steel, so as to provide a guidance for the application of this method in the 9310 steel gear shaft wear repair. A comparative experiment is conducted on the bending fatigue limit of 9310 steel specimens using four different surface treatment methods:carburizing, chrome plating, spraying WC-17Co, and spraying WC-10Co4Cr. The influence of different surface treatment methods on the bending fatigue performance of 9310 steel is obtained through a data analysis. At the same time, a failure fracture analysis is conducted to reveal the fatigue failure mechanism. The research shows that the bending fatigue of shallow infiltration layer samples (0.7-0.9 mm) is 731.2 MPa, furthermore the bending fatigue of deep infiltration layer samples (1.25-1.50 mm) is 887.5 MPa. The bending fatigue of deep infiltration layer samples is 21.38% higher than that of shallow infiltration layer samples, and the fatigue cracks of the samples originate from the surface. The bending fatigue of the chrome plated sample is 368.7 MPa. Compared with the 9310 steel sample with the same penetration depth, the bending fatigue decreases by 58.5%. The fatigue life decreases with the increase of the chrome plating thickness, and the fatigue cracks originate between the sample body and the coating. The bending fatigue of WC-10Co4Cr sprayed sample is 720.8 MPa, which is 18.78% lower than that of 9310 steel sample with the same infiltration layer depth, the fatigue crack originates between the sample body and the coating. The bending fatigue of the WC-17Co sprayed sample is 875 MPa, which is basically equivalent to the 9310 steel sample with the same infiltration layer depth, and the fatigue crack originates from the surface of the sample. All failed fracture surfaces exhibit typical fatigue fracture characteristics. There are numerous secondary cracks and cleavage planes in the steady-state crack propagation region and large areas of intergranular cracks and secondary cracks in the rapid crack propagation region. Additionally, there are many ductile dimples of different sizes in the transient fracture region. The surface chrome plating treatment method greatly reduces the bending fatigue strength of the sample, and this method is not recommended for repairing the worn surface of gear shafts. The surface spraying WC-10Co4Cr treatment method reduces the bending fatigue strength of the sample to a small extent. When applying this method to repair gear shafts, caution should be taken and the strength should be evaluated. The surface spraying WC-17Co treatment method has minimal impacts on the bending fatigue limit of the repaired parts and can be widely used for repairing the worn area of 9310 steel gear shafts.