Numerical simulations were applied to study the leakage flow of assembled endwall slot of turbine guide vane of an aero-engine. The effects of leakage flow on the structure of flow field of cascade passage and performance parameters of the cascade were also discussed. The leakage flow pressures

the slot width and position of the slot were changed to investigate the rules of leakage flow rate and energy loss coefficient varying with these parameters and discover the effect rules. It is found that the leakage can appear due to different pressures between cooling air and gas

spiral vortex system is formed in the middle position of the slot at the same time

and the leakage flow affects the secondary flow around the endwall significantly. The effect decreases along the direction of blade height and the largest region is up to 44.44% of the blade height. With the increase of leakage flow pressure

the slot width and the angle between the slot and major axis of engine

the energy loss coefficient of the cascade and the leakage flow rate increase monotonically. Numerical results show that the energy loss coefficient of the cascade increases by 14%-62% because of the leakage flow through the slot of the endwall in the parameter range of present study.