The flow field of a certain proportional multiway valve were analyzed by using fluid dynamics software Fluent. The results of analysis shows that the valve inlet pressure drop is most obviously, the largest velocity increased significantly, the cavitation phenomenon is occurred around the valve corner. The valve core structure factors influence on these results was analyzed, and opening K shape notch on the valve core was optimized, the results shows that the valve cavity flow more smoothly after the optimized structure. Finally, the improved valve core was carried on the finite element analysis by using the fluidstructure interaction technology on workbench, it is concluded that the shape of valve core variable distribution and temperature distribution to consistent with the practical test results, and provided an important basis on choosing the structure and material of valve core.