Accurate control of both the timing and quantity of injection events is critical for engine performance and emissions.The most serious problem,which reduces the accuracy of the control operation in such systems,is time-delay of the responsiveness for the opening and closing operation of the electromagnetic valve.In this paper,the dynamic characteristic of a high-speed servo-hydraulic solenoid injector for diesel engine,with different driving methods,was investigated.The solenoid current was measured to get the electrical delay of the injectors.Meanwhile,high-speed photography was employed to detect the total delay(electrical delay,hydraulic delay and mechanical delay)of the injection spray process.The results show that,there is a high correlation between the opening delay and the solenoid current,the armature of the injector will not move until the current rate of change reaches the maximum valve.Based on pressure curve of the injector nozzle inlet,the delay of opening and closing of needle and injection duration can be calculated.Measurement of solenoid current and nozzle inlet pressure will provide boundary conditions for injector design and calculation in the future.