In order to ensure and improve the performance of the fuel vapor-containment system (FVS) on a hybrid electric vehicle (HEV), the vapor pressure field of the evaporative (EVAP) system in the refueling process was analyzed. Numerical models were established to describe the pressure change in the EVAP system. Based on these numerical models, the influences of refueling speed, filler pipe diameter, vent pipe diameter, and fuel vapor-containment valve (FVV) port diameter on pressure change were discussed. The numerical models and the influences of aforementioned effects were validated by experiments. Simulation and experimental results indicated that the vapor pressure field in the EVAP system is more susceptible to the change of refueling speed and FVV port diameter. If the refueling speed increased and the FVV port diameter decreased, the vapor pressure in the EVAP system strongly fluctuated. Furthermore, results also show that the FVV port diameter should be as large as possible but less than 20 mm, while refueling speed should be 50 l/min. The filler pipe diameter can be chosen in the range of 23–28 mm.