In this article, an energy conversion system suitable for the magnesium seawater batteries is designed. To address the problems of soft output characteristics and low voltage of magnesium seawater batteries, the conventional non-isolated three-port converter is optimized to improve the voltage gain. Based on this converter topology. Considering the output characteristics of magnesium seawater batteries and the load characteristics, an energy management strategy for DC/ DC converter system suitable for sudden load change is proposed. By controlling the flexible flow of energy between any two ports in the system, the dynamic power balance of source and load is achieved. Meanwhile, according to the output characteristics of magnesium seawater batteries, a maximum power point tracking method based on the improved grey wolf optimization is introduced into the system energy management, which further improves the energy conversion efficiency of the magnesium seawater batteries. Finally, simulations and experiments demonstrate that when the load power changes between 0. 36 and 1. 2 W, the converter can complete the mode switching accordingly. On the premise of ensuring the output voltage is stable at 12 V, the flexible control of the output current of 30 and 100 mA is realized, which verifies the rationality of the hardware and software design of the energy conversion system.