In order to study the influence of the smooth labyrinth seal structure on sealing performance,which is used in supercritical carbon dioxide spray dyeing device,the flow field of carbon dioxide internal the labyrinth seal was simulated with FLUENT,the motion and energy conversion of carbon dioxide in the the labyrinth seal were analyzed.The influence of throttle gap size,sealing tooth shape and tooth top round size on the sealing performance of labyrinth seal was discussed.The results show that the sealing performance of labyrinth seal has linear relationship with the throttle gap size,and the sealing performance becomes better with decreasing the size of throttle gap.The labyrinth seals with three shapes,such as parallelogram,isosceles trapezoid and back trapezoid,have better sealing performance,among of them,the trapezoidal throttle teeth has the best comprehensive performance.With the decreasing of the size of tooth top round,the resistance of carbon dioxide flow through the labyrinth seal is increased,the sealing of the labyrinth seal is improved.