When adjusting the transmission power of the dual-bridge series resonant converter (DBSRC) under the phase-shift modulation, significant step changes in phase-shift angles may occur. These changes stimulate a long-time oscillation process in the resonant tank with a large amplitude appearing in inductor current and capacitor voltage. During this transient process, the converter's dynamic performance deteriorates considerably, and the circuit components may experience severe overvoltage and overcurrent. In view of that, this article develops a transient process calculation model (TPCM) for the DBSRC using the fundamental harmonic approximation to analyze the oscillations during the transient process. Subsequently, the peak capacitor voltage, the peak inductor current, and the settling time during the transient process are estimated. Furthermore, based on the TPCM, this article proposes a control method to make the converter reach a steady state after one switching cycle, thus avoiding the risk of overvoltage and overcurrent and greatly improving the dynamic performance of the converter. Finally, the results of the theoretical analysis and the proposed control method are verified by simulations and experiments.