Switching hydraulic inertial systems (SIHS) manipulate the interaction of inertial and capacitive components through switching valves to achieve the efficient and rapid pressure regulation. However, the opening and closing of the switching valve lead to fluid expansion and compression in the switched volume, which generates throttling losses in the switching valve transition cycle, resulting in substantial energy loss. Hydraulic soft switching is an essential means to solve the loss of switching valves. However, the poor resonance performance of the hydraulic system leads to arduousness in the soft switching design. Therefore, this paper proposes that a mechanical-hydraulic coupling mechanism can realize the soft switching. A new approach is proposed to realize soft switching with a parallel double-motor mechanism based on the new idea. The approach connects inertive elements, at the back, to the switching valve to suppress the sudden flow increase caused by the compressed fluid in the switched volume during the opening transition stage of the switching valve, thus effectively reducing the loss caused by the throttling flow of the switching valve. The new approach has been experimentally verified to reduce the throttling flow by 33%, resulting in an increase of the SIHS output efficiency by 10%–15%.