Abstract: The gamma radiation field was theoretically simulated by Monte-Carlo method for the hypothetical plutonium components in the condition of different pinhole image collimators. The passive gamma ray pinhole image method was studied in order to measure the symmetry attribute of plutonium component. Simulation results show that the quality of image can be improved by using the optimized pinhole collimator, and the sensitive information such as pinhole collimator parameters, object distance, image distance should be treated as barrier information to prevent the release of them.