The application discloses a synthetic lubricating oil for food machinery and a preparation method thereof, wherein the lubricating oil includes natural gas synthetic oil, alkyl naphthalene base oil and other additives. All ingredients in this application comply with FDA regulations 21CFR178 3570, all components are safe and non-toxic, and meet the national food-grade lubricant hygiene requirements, and the food-grade multi-purpose oil prepared based on this component can be used in food processing On equipment or mechanical parts that may have accidental contact with food, meet the requirements of the US Sanitation Foundation NSF H1 category lubricants. Reasonable composition, good viscosity-temperature performance, high oil film retention, outstanding lubricating performance; outstanding thermal oxygen stability, long service life; outstanding anti-wear, anti-rust, anti-corrosion, water resistance and other properties, strong versatility, can meet the needs of food processing The lubrication needs of various lubrication places in the process simplify inventory management, and it is non-toxic and harmless, and has no pollution to food. Even if there is volatilization or leakage of mechanical equipment, it will not pollute the product and affect food safety.