Abstract: The field distributions, in the electron multiplier with eight stages of box-shaped grid-dynode assembly, were mathematically modeled, theoretically analyzed and numerically simulated with CST software.The influence of the box-shapes, including the boxes with a top-view of pentagon, square, quarter-circle and triangle, on the electric field profiles, electron trajectories and multiplication gains was investigated.The simulated results show that the box-shape has a major impact.To be specific, the impact factor of the box-shapes can be listed in a descending order:pentagon>square>quarter-circle>triangle.Theoretically speaking, the multiplication gain decreases from 835 to 65, because no secondary electron emission coatings are deposited on the two short-sides of the pentagon dynodes, made by truncating the two sharp angles of a right-angled triangle.We suggest that the simulated results be of some technological interest in design of box-type electron multiplier.