[en] [Background] Calcium silicate products were used as thermal insulation for China Experimental Fast Reactor (CEFR) cock, which might in contact with sodium vapor and liquid sodium. [Purpose]This study aims to investigate the compatibility of calcium silicate thermal insulation with sodium and sodium vapor. [Methods] First of all, gloves box purified by argon circulating and static testing facility of high temperature sodium were employed to build a test platform. The tests of the compatibility of calcium silicate insulation with high temperature sodium vapor and sodium at 250℃ for duration ranges from 3 min to 1500 h. After the test, some examinations include surface morphology analysis, cross section morphology analysis and thermal conductivity were performed. [Results] The results show that there is no fierce reaction occurred between calcium silicate insulation with sodium and sodium vapor. Varitions of color and appearance only appear on the surface of the samples, not inside the sample. During the fabrication process of the insulation post-test, the samples do not become brittle or soft. The thermal conductivity of the samples remains constant before and after the test, sodium and sodium vapor have no effect on the thermal insulation property of samples. [Conclusions] The calcium silicate has good resistance to sodium and sodium vapor corrosion. (authors)