Abstract: In order to build a very-low-level γ ray radiation field and its magnitude transfer system, the scattering contribution caused by different mechanical device structure is researched based on the experimental conditions of the Jinping underground laboratory in China. In this research, the Monte Carlo model of the irradiation device, the magnitude transfer detector, and the internal transmission structure of the shielding box were built in the MCNP5 software. After that, the scattering contribution caused by three spatial variables: the emission angle of the irradiation device, the distance between the detector and the edge of the shielding box, and the distance between the source and the detector, was simulated, and the appropriate device design and layout scheme were obtained. The emission angle of 20°, 30° and 40° were used in this research. The energy deposition in sensitive area (with/without the shielding box) was recorded under three different distances between the source and the detector. Three locations of the irradiation device were designed to analyze the change of energy deposition caused by the change of locations. The energy deposition in sensitive area was simulated under more distances between the source and the detector. According to the data, the increase in energy deposition with the emission angle of 20° is less than that caused by the emission angle of 30° and 40°, and the increase in energy deposition is less when the irradiation device is far from the edge of the shielding box. In this research, energy deposition caused by scattering radiation under various irradiation conditions were obtained and analyzed, the device design and layout in the radiation field were optimized, and the idea for establishing an extremely-low-background radiation field was provided.