In order to design a labyrinth seal with better sealing performance, the numerical investigation is applied. The solution to the incompressible Navier-Stokes equations in velocity-vorticity formulation is calculated by means of finite element method. The velocity vector field, the vorticity field and average pressure in the seal cavity of the labyrinth seal in the air blower are studied. The regularity of pressure changing in the seal cavity with the main geometric sizes of the labyrinth seal changing is calculated. And finally, the effect of the main geometric sizes of the labyrinth seal on the leakage is deduced. These results offer the theoretical guidance for designing a better labyrinth seal.