The invention discloses biodegradable lubricating oil. The biodegradable lubricating oil comprises base oil, an anti-oxidant, a rusting inhibitor, an anti-foaming agent, a metal deactivator, a demulsification agent, an antiwear agent, a cleaning agent, a viscosity index improver, copper oxide powder and magnesium metal powder. The anti-oxidant is a mixture of diarylamine and dithiocarbamate. The rusting inhibitor is an alkylsuccinic acid derivative. The anti-foaming agent is a dimethyl siloxane polymer. The metal deactivator is triazole. The demulsification agent is polyalkoxypolyphenol. The antiwear agent comprises alkyl phosphate ester and salt. The cleaning agent is calcium petroleum sulfonate. The viscosity index improver is an ethylene-propylene copolymer. The biodegradable lubricating oil is prepared by a simple method, has high quality, a long use period, improved extreme pressure resistance, and completely improved oxidation resistance, corrosion resistance and foaming resistance, can be degraded biologically and completely exceeds environmental protection requirements on the same type of products.