In order to analyze the performance of the helical seal with the nonNewtonian fluid as seal medium,taking powerlaw fluid as the research object and based on CREASE’s sealing capability equation for Newtonian liquid lubricated helical seal,the sealing capability equation for powerlaw fluid lubricated helical seal was obtained with approximate analysis method by replacing the velocity distribution equation of the two dimensional steady flow of Newtonian fluid with the velocity distribution equation of the two dimensional steady flow of powerlaw fluid.A comparison was made with the results for this approximate analytic method and the numerical simulation by Fluent software,which showed the results between the two methods were consistent.The influence of operating parameters and geometric parameters on the sealing capability was analyzed by the approximate analytic method.The results show that the sealing capability is increased with the increasing of flow behavior index,consistency coefficient and shaft speed,and increased at first and then decreased with the increasing of spiral angel,relative groove width and relative depth.