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This paper made a comprehensive allocation of waste heat from W7X82DF model low-speed two-stroke marine Dual-Fuel engine regarded to its exhaust gas and jacket water waste heat and energy grade, and developed a combined organic Rankine cycle (ORC) system which can effectively utilize the cold energy of liquefied nature gas (LNG) and the waste heat of dual-fuel marine engine. Apart from that, we take the actual situation of heat transfer temperature difference into full consideration, and performance of twelve low-carbon green refrigerants with the situation that the value of ozone dissipation potential equal to 0 and global warming potential is less than 150. Through the closed circuit of the exhaust gas conversion device, the waste heat of the exhaust gas is driven to high-temperature cycle. Due to the advantages of large and stable flow of jacket water, and constant inlet and outlet temperature, it can be used as the heat source of low-temperature cycle to recover the waste heat of jacket water. The process simulation software Aspen Plus was used to build the cycle, and the P-R equation physical property method was selected. According to the simulation curve, the following conclusions are drawn: R600a is more suitable as working medium of High-temperature cycle, thermal efficiency and net output power are 10.43% and 399.061 kW; The R600 is more suitable as the working medium of Low-temperature cycle, with the thermal efficiency and net power output of 12.88% and 340.13 kW respectively. Through the research in this paper, it provides a reference for the waste heat recovery of marine engine and improves fuel utilization and economy.