Abstract: The relationship between the direction vectors of the sun light at the lunar surface and those at the detector surfaces in a lunar crater are derived through a coordinate transformation. Radiative heat fluxes at the detector surfaces are numerically computed using the Monte Carlo method, and the ambient radiative heat flux distribution in lunar craters is analyzed. Spacial and temporal distribution characteristics of radiative heat fluxes at the detector surfaces and the influences of some parameters on the flux distribution are discussed, including the lunar latitude, the crater diameter, the lunar surface emittance. Computational results show that both the increase in the lunar latitude and the decrease in the crater diameter will make the sun light unattainable in the crater bottom during a certain time periods, resulting a significant difference in the operating conditions. But these two parameters influence the detector surface fluxes in different ways. In addition, the detector surface fluxes are influenced significantly by the lunar surface emittance. With the increase in the lunar surface emittance, the radiative heat fluxes on certain detector surfaces decrease obviously.