Abstract: In order to provide the reference for the structural design of Compton imaging system, the method to estimate the scattering angle error of Compton imaging system composed of two-layer position-sensitive CZT crystal by combining theory with simulation calculation was presented, and the scattering angle error of the Compton imaging system was studied by this method. The results show that for incident photons of 662 keV, 1.33 MeV and 2 MeV, the Compton scattering angle errors are 5.54°, 4.82° and 4.52°, respectively. The scattering angle error mainly comes from the position and energy resolution abilities of the detection system, and the contribution of the angle error caused by the Doppler effect of the detection material is relatively small. Limiting Compton scattering angle range reasonably can improve the angular resolution of imaging system and optimize the imaging effect effectively.