Abstract: A series of experiments of single phase natural circulation under inclination conditions were performed using the test facility of integrated reactor and followed RELAP5 numerical analysis. The result shows that RELAP5MOD3.2 can accurately predict the mass flow rate of natural circulation under inclination. Mass flow rates of primary side of heat exchangers showes a different variation trend when lateral inclination, mass flow rate of the higher heat exchange is larger than that of lower heat exchanger. The larger the deviation angle of heat exchangers and heaters in vertical direction, the greater the difference of mass flow rates between heat exchangers. The mass flow rates of each section changed in the same way when the longitudinal inclination and the mass flow rate decreased dramatically as inclination angle increased. The total natural circulation mass flow rates of lateral and longitudinal inclination in the same angle are very close.