Monte Carlo method was used to study the shielding characteristics of ship compartments in early nuclear radiation scenarios. Using early gamma radiation as a radiation source, the mass attenuation coefficients of three commonly used materials, HSLA-80, 5456Al, and FDCL-3B, for ship bodies were measured. A simulated cabin model was established based on the geometric structure of the ship, and Gaussian broadening method was used to fit the detector's energy spectrum. The absorption energy spectrum of the NaI detector inside the cabin under gamma radiation was obtained, and compared with experimental results in the literature, thus verified the reliability of the calculation model and results. On this basis, using the gamma protection coefficient as the evaluation index, considering two scenarios of radioactive isotopes (single energy point sources) and early gamma radiation (surface sources with energy distribution), the spatial distribution characteristics of gamma radiation shielding in simulated cabins were calculated and analyzed. The results show that the protection coefficient of the simulated cabins for different radioactive isotopes was different, with a maximum difference of 6.74 times (Cd-109 and Cs-137); The protection coefficient varies in different positions of the cabin. The gamma radiation dose at the front end of the cabin is relatively high, while the gamma radiation dose at the corners is relatively low, with a difference of 35%; The protection coefficient is related to the incident angle of gamma irradiation. Compared with normal incidence, the simulated cabin has a higher gamma radiation protection coefficient for oblique 45° incidence, which can be improved by 43%.