Abstract: In order to study the influence factor and ease measure to thermal stratification intensity in feed water ring and pipe of steam generator in low power operating condition of PWR NPP, thermal stratification in feed water ring and pipe of steam generator was simulated by using computational fluid dynamics (CFD) method. Some factors to have influence on thermal stratification intensity were studied and two improved structures were proposed from the aspect of the layout and structure of feed water ring and pipe. The results show that increasing mass flow rate of feed water can not ease the thermal stratification intensity in feed water ring and pipe of steam generator during the power increasing condition, increasing curvature radius of the feed water elbow can ease the thermal stratification intensity in the feed water elbow effectively, changing the direction of feed water downward can ease the thermal stratification intensity in the feed water ring and pipe obviously, and increasing the lean angle of feed water pipe can ease the thermal stratification intensity in the feed water pipe but enhance it in the feed water ring. Changing the direction of feed water elbow downward and changing the horizontal pipe into multistage laddered divergent-convergent structure and multistage spherical divergent convergent structure can ease the thermal stratification intensity in feed water ring and pipe in varying degrees during the power increasing condition, so these two improved structures are ideal improved structures.