A new type of environmentally friendly chelated borate-alkyl imidazole ionic liquid (n-DICB/i-DICB) was developed with 1,3-didecylimidazole as the cation and dis-salicylic acid chelated boric acid as the anion.The tribological properties of the two additives in the base of trimethylolpropane trioleate (PETO) were investigated using a four ball tester.The morphology of the worn surface and the chemical composition of the friction film formed during friction were analyzed by SEM,EDX and XANES.The results show that n-DICB/i-DICB additives have excellent tribological properties and can significantly improve the friction reducing,anti-wear and extreme pressure properties of the biodegradable base oil.I-DICB has better antifriction performance and extreme pressure performance than n-DICB,and mass fraction 2.5% of i-DICB can reduce the friction coefficient and wear scar diameter of PETO by 33.0% and 22.1% respectively,and increase the maximum non seizure load by 66.6%.During the friction process,n-DICB/i-DICB forms a compact friction film mainly composed of a mixture of B2O3,Na2B4O7,NaBO3 and BN,which contributes to the excellent friction properties of the ionic liquids.