n the process of helicopter design finalization flight test, the reducer is a very important component in the helicopter transmission system, and its performance has a great impact on the safety of the helicopter. The gear transmission system of the reducer usually works in high speed, high temperature, heavy load and other harsh environments. At the same time, due to the complexity of the transmission gear itself, it is easy to cause gear tooth structure to break, peel and other failures, which seriously affects the stability and reliability of the helicopter transmission system. In this paper, through the identification of typical faults of the transmission gear of the reducer, combined with the theory of finite element analysis and gear meshing, the finite element model of the reducer gear transmission in the helicopter is established, and the stress distribution and change under the typical fault of the transmission gear are analyzed, which provides a new idea for the fault monitoring and testing technology of the helicopter transmission system.