In order to investigate the effect of high-pressure conditions on the control-valve of common rail injector, a sealing reliability test was carried out in a conventional type of common rail injector, and an unsteady vapor-liquid two-phase flow CFD simulation about the control-valve was performed with AVL—Fire. The displacement measurement of armatur-pin of solenoid-actuator was accomplished for the boundary condition setting of computational dynamic grid. The simulation was validated against the experimental result of fuel backflow measurement in terms of mass flow rate. The reliability test result shows that cavitation damage appears on the conical seat surface of control-valve. The simulation result demonstrates that obvious cavitation phenomenon occurs in the guide-hole of the control-valve when inlet pressure boundary condition is increased to 250MPa level. It also indicates that at three typical inlet pressure levels, viz., 150MPa, 200MPa and 250MPa, the ratio of mass exchange rate of vapor-liquid phases is 1∶1.187∶1.437. With respect to time dimension, the mass exchange rate reaches a peak at the incipient stage of closing course of the control-valve.