The invention discloses a gear engagement fatigue testing device, and the device comprises a drive apparatus fixed on a foundation table, a simulation load apparatus, and a test gear apparatus. The drive apparatus and the simulation load apparatus respectively cooperate with the test gear apparatus, and are respectively connected with a central controller. The central controller controls the drive apparatus through outputting a displacement time curve signal, and controls the simulation load apparatus through outputting a load time curve signal. A brand-new loading process is employed to convert the meshing in a rotation process of a gear pair into the meshing in a reciprocating swinging process. The actual process of gear transmission is simulated, and a high-frequency big-period test can be carried out for a single tooth. The small-amplitude movement facilitates the building of the test apparatus, and the real-time performance and accuracy of stress and strain data collection in a gear failure process. The device is high in automation degree, is good in testing quality, is novel in testing loading method, and is suitable for the measurement of the related data in the gear transmission process.