Abstract: Large thick aperture imaging method was proposed to measure the radiation intensity distribution of radiation source whose size is several centimeters. The new method contains two steps, which are coded imaging and image reconstruction. Geant4 was used to simulate the coded imaging process. Matlab was used to simulate the image reconstruction process using inverse filtering, Wiener filtering and Lucy-Richardson method. The input parameters of Wiener filtering and Lucy-Richardson method were optimized according to the root mean square error. They were applied to reconstruct the coded imaging of 5, 10, and 15 mm aperture respectively. Inverse filtering causes noise amplification, and Wiener filtering produces artifacts. Lucy-Richardson method can give out a clear restoration image. The root mean square error of the reconstruction image using Lucy-Richardson method is 15% larger than that using traditional pin-hole imaging method. It implies that large thick aperture imaging method can get a similar result with traditional pin-hole imaging. The new method is proved to be effective.