Abstract: A series of dimmer acid esters were synthesized by using dimmer acid and different chain length alcohols, and the molecular structures of synthetic dimmer acid ester were identified. Their rheological and tribological characteristics were evaluated and analyzed. Tribological compatibility of different antiwear additives was evaluated and analyzed with Di-iso-octanol dimmer acid ester as base oil. At the same time, main element of the worn steel surface was analyzed. Biodegradability of different base oils was tested according to DIN-51828-1,2. Results show that viscosity temperature property of synthetic dimeric ersters has good performance. Viscosity increases and pour point decreases with alkyl chain, and pour point of branching dimeric ester is much lower. Antiwear property and loading ability increase with the alkyl chain. Antiwear property and loading ability of dimeric esters with the same length of alkylchain increase with isomerization. Integrated characteristics of Di-iso-octanol dimmer acid ester are the best among the synthetic dimmer esters. Its rheological and tribological characteristics are better than that of Pentaerythritol esters (C7~9 acidate). It is a kind of base oil with good properties and it is biodegradable.