Taking the choma seal in the entrance section of mine drainage pump as research object,the flow characteristics of internal flow field of labyrinth seal were analyzed by numerical simulation method.The effects of structure sizes and sharps of labyrinth seal on the leakage were analyzed.The results show that the effect of labyrinth clearance size on sealing performance is the largest,the changes of clearance width and throttling tooth width will lead to the large change of leakage.Compared with the labyrinth seal of straight tooth,the labyrinth seal of special shaped tooth can improve the sealing performance,for its structure is conducive to the sufficient development of turbulence.The optimum structure of labyrinth seal for the drainage pump was got by studying the complex internal flow of labyrinth seals.