Abstract: To address the leakage issues prone to occur in the main shaft seals of vertical vacuum agitators under special operating conditions, and the inadequacy of existing sealing methods in effectively resolving this problem, a novel labyrinth-magnetohydrodynamic composite sealing device has been designed. Using finite element numerical simulation, the magnetic field distribution patterns within the sealing gap were investigated, yielding a theoretical pressure resistance value of 0.375 MPa for this device. Single-factor analysis was employed to investigate the effects of seal clearance, tooth slot width, pole tooth height, and pole tooth width on the seal's pressure resistance. Response surface optimization was then used to refine the structural parameters. Results indicate that the seal's pressure resistance initially increases with greater pole tooth height and width before decreasing; decreases with increasing seal gap; and increases initially then stabilizes with increasing tooth slot width. The optimized seal parameters are: seal gap 0.1 mm, pole tooth height 1.89 mm, pole tooth width 1 mm, and tooth slot width 3 mm. The resulting seal pressure resistance reaches 0.555 MPa, significantly exceeding the operational pressure requirements and meeting sealing demands.