In this study, a method for improving the exhaust energy grade called exhaust energy splitting is proposed. During the exhausting process of a low-speed marine diesel engine, the exhaust energy splitting is used to split and recover the exhaust in the early stage and the sweeping gas in the late stage separately. GT-Power software and Flowmaster software are used to co-simulate and design the exhaust energy splitting system. Through exergy analysis of the exhaust piping system before and after the energy splitting, the exergy efficiency of the system increases by about 0.47–4.92%, and the optimal splitting phase is around −115 deg. At the same time, the exhaust splitting system is optimized from the perspectives of heat exergy and kinetic energy exergy, and the results show that the exergy efficiency of the optimized exhaust piping system improves by 0.2–2%. This paper demonstrates the feasibility of exhaust energy splitting through exergy analysis.