Abstract: To study the impurity accumulation phenomenon and corresponding impact on head loss through fuel assembly after loss of coolant accident in Pressurized Water Reactors (PWRs), the test platform is established and the distribution and blockage of debris in the assembly  in the worst condition were analyzed, and the effect of the debris in the containment after LOCA on the pressure drops across a fuel assembly is quantatively evaluated. All test results indicated that almost all debris were captured on the lower half of the fuel assembly, especially on bottom nozzle. The head loss resulted from debris added with concurrent addition method was higher than that with sequential addition method with the same debris amount; The chemical precipitate could compact the debris bed, resulting in a great effect on head loss; Enough coolant could be provided into the core for cooling even in worst condition.