Abstract: To accurately measure the secondary electron yield (SEY) is of great significance for studying the charge and discharge of spacecraft surface materials. The electron transmittance through grid in the secondary electron measurement device is an important factor affecting the measurement accuracy of the SEY of materials. In this paper, the causes of influencing the electron transmittance through grid in a multi-layer spherical SEY measurement device was simulated by calculation, and the geometry parameters of grid were optimized. The results show that the grid bias exhibits little effect on the electron transmittance through grid, whereas the grid geometry parameters are the main influencing factor. When the grid wire is 0.025 mm in diameter and the grid spacing is 1 mm, the electron transmittance reaches the maximum. The proposed research may provide a reference for optimizing the design of SEY measurement device.