Penumbral imaging of the neutron production in laser-driven inertial confinement fusion experiment is an important diagnostic technique. In order to meet the resolution requirement, we simulate the point spread function (PSF) under the conditions of different source-aperture distances, different thicknesses, different outer radii, and different shapes of the aperture. Base on the sharpness and the isoplanaticity of PSF, the diagnostic system can be optimized. According to the simulation results, tolerant misalignment of system is analysed: a resolution of 15 μm can be satisfied by the linear reconstruction method, and a resolution of 5 μm can be achieved by using the nonlinear reconstruction method.