Recently, due to regulations on emissions of vessels, fuel is changing to liquefied natural gas (LNG). When using LNG as fuel, it is advantageous in terms of fuel saving and boil-off gas control if a small-scale liquefaction process is installed on the ship. However, due to the limited space, the small-scale liquefaction process for ships has to consider not only efficiency but also simplicity and compactness. In this respect, it is different from the process in onshore liquefaction plants, and research on this is insufficient. Therefore, this paper performs a comparative analysis in terms of efficiency by simplifying the composition of the mixed refrigerant in the liquefaction process. Additionally, a single mixed refrigerant process is used to pursue the compactness of the process. For comparative analysis, the liquefaction process is designed and simulated, and the specific power consumption calculated as the power required to liquefy the unit LNG is used as the objective function to optimize. As a result, it is confirmed that when the number of refrigerants is reduced from 5 to 4, the efficiency is only about a 1% difference, but when it is reduced to 3, the efficiency decreases by 23%, resulting in a decrease in performance.