Abstract: Thermal stratification of pressurizer surge line induced by the inside fluid results in the global bending moments,local thermal stresses,unexpected displacements and support loadings of the pipe system.In order to avoid a costly three-dimensional computation,a combined 1D/2D technique has been developed and implemented to analyze the thermal stratification and fatigue stress of pressurize surge line of QINSHAN Phase II Extension Nuclear Power Project in this paper,using the computer codes SYSTUS and ROCOCO.According to the mechanical analysis results of stratification,the maximum stress and cumulative usage factor are obtained.The results indicate that the stress and fatigue intensity considering thermal stratification satisfies RCC-M criterion.