The flow field of non-circumferential opening spool valve with single U-shaped notches was simulated based on RNS κ-ε model,the calculation results were post-processed by using field synergy theory,mechanical energy consumption principle and Ω vortex identification method,and the distribution characteristics of the flow field parameters in the notches of different flow directions were analyzed.The results reveal that the energy consumption of the throttling slot in the inflow direction is mainly caused by the flow acceleration at the inlet of the notches,the liquid-solid impact of the flow jet,the centrifugal effect vortex and the flow deceleration at the outlet of the notches; the energy consumption in the outflow direction is mainly caused by inlet acceleration,vortex in slot and outlet flow deceleration.The difference of energy consumption mechanism in different flow direction leads to the inconsistency of flow coefficient and flow hysteresis phenomenon.