Abstract: Space radiation is one of the most important risk factors for the health of astronauts in the long-term manned spaceflight. In order to develop reasonable space radiation protections in the manned lunar explorations, the space radiation field models are used to simulate and calculate the physical characterizations of the space radiation in the spacecraft cabin with different thicknesses of the shielding materials during the Chang'e-3 mission to the Moon, and the radiation doses, the dose equivalents and the effective doses of each organ of the astronauts are determined to evaluate the space radiation risk. The results show that the adsorbed doses, the dose equivalents and the effective doses decreases significantly with the increase of shielding thicknesses, and the mass shielding method has a very good protective effect for protons with energy below 100 MeV, while the effect is not significant for high energy protons or heavy ions. The calculation and analysis show that the space radiation risk of astronauts can be controlled in the manned lunar exploration mission as long as the appropriate shielding is adopted in the spacecraft or spacesuit.