Abstract: Taking a certain helical gear pair in aero gearbox as the research object, the gear modification is analyzed with KISSsoft software. The helical gear tooth is modified by suitable method, the meshing performance and contact analysis of the gears before and after modification are studied, mainly comparing the parameters of the tooth strength, transmission error, tooth surface load distribution and sliding ratio. It is concluded that reasonable modification on the inclined gear can improve the endurance capacity and the meshing performance of gear, and can reduce the excessive roof, root overload and the load mutation phenomenon; thus it effectively improves the meshing quality. Through the comparative analysis with the actual gear contact pattern, it shows that the analysis results of KISSsoft are effective and reliable.