The labyrinth seal model of high speed gearbox transmission shaft was established. The standard k-ε turbulence model was used to simulate the flow field characteristics in the labyrinth seal, and the leakage, pressure and velocity distribution were analyzed. Simple algorithm in Fluent is used to calculate the energy equation and turbulence equation. By studying the influence of tooth pitch and tooth tip length on sealing performance, the optimal parameters were determined. At the same time, the influence of inlet pressure and speed on the leakage of labyrinth seal of gearbox was studied. The results show that the leakage increases with the increase of tooth pitch. With the increase of tooth tip length, the leakage quantity decreases at first and then remains basically unchanged. When the temperature rise condition is not considered, the speed has almost no effect on the leakage, but with the increase of the speed, the sealing performance improves.