The electrical control common-rail injector (CRI) is a key component in marine diesel engines. Herein, a detailed fluid-mechanical-electric-magnetic coupling mathematic model regarding the CRI was established, considering the transient of fuel properties, different structure parameters of the CRI, and the nonlinear magnetization and magnetic saturation of magnetic materials of the high-speed solenoid valve (HSV) for the CRI. This model was verified by comparing the calculated injection rate with the experimental data at different injection pressures, and the good consistencies obtained proved the validity of this model. Based on this model, the effect of different factors on the dynamic response of the injector was investigated to prepare for the optimization. The results demonstrated the different structure parameters of the injector, such as the diameters of the inflowing control orifice (OZ) and outflowing control orifice (OA), maximum needle displacement, diameter of the control plunger, and driving strategy, influenced the dynamic response of the CRI with varying degrees. For the open response, the influence degree from high to low is the diameter of the control plunger, OA, OZ, maximum needle displacement, and boost voltage; for the close response, it is the control plunger, OZ, maximum needle displacement, and hold current. The influence degree of the structure parameters is always stronger than the driving strategy. Establishing a detailed mathematic model is helpful to study the influence of different factors, and an effective optimum design for an injector and its HSV is proposed in detail.