The porosity and pore size distribution of coral sand concretel(CSC) were analyzed by a microparticle mercury porosimeter. The influence of temperature and relative humidity on the thermal conductivity of CSC was studied. The functional relationship between the thermal conductivity of CSC and the relative humidity, the water absorption coefficient and the moisture sorption isotherms of CSC were obtained. The results show that the porosity volume fraction of CSC is 28.76%, and the maximum growth rate of pore volume is 3040nm. The temperature has little effect on the thermal conductivity of CSC in the dry state at -2050℃, the maximum change rate is only 055%. At 25 and 35℃ with the relative humidity of 0%100%, the change process of the thermal conductivity of CSC can be divided into the steady rising stage, the gentle increasing stage and the rapid increasing stage. When the relative humidity changes from 0% to 100%, the thermal conductivity of CSC increases by approximately 295% and 490% at 25 and 35℃, respectively.