Abstract: Penumbral imaging has high sensitivity, which will be the main technical method of neutron imaging in inertial confinement fusion (ICF) experiments. Based on the requirement of neutron penumbral imaging, two-dimensional image of neutrons transport in the coded aperture is simulated by Monte Carlo method, with the biased sampling skill and surface-flux replaced by volume-flux skill. The source image is obtained by reconstruction program. According to the simulation result, the 5 cm thick W bulk is selected as the shileding material and the optimized aperture outer radius is 1 cm.