Abstract: The one dimension mathematics model is established for the diffusion of sodium water reaction products in steam generator (SG) and leak detection system (LDS) for liquid metal cooled fast breeder reactor. The effects of sodium temperature and flowrate of SG and LDS are analyzed and the useful results are obtained from numerical calculations and experiments in a sodium loop. The results show that increasing the sodium flowrate of SG and LDS, the response time of LDS is decreased, but the sensitivity is lowered. The effect of sodium temperature of SG on the response time of LDS is less than that of sodium flowrate in SD, however, it can make the sensitivity of LDS higher when the sodium temperature is raised.