Abstract：The environmentally-friendly plasticizer tri-n-octyl maleopimarate(n-TOMP) was synthesized by the reaction of Maleopimaric acid (MPA) with n-octanol using p-toluenesulfonic acid(PTSA) as catalyst and n-octane as water entrainer. The optimal reaction conditions were as follows: n(MPA):n(n-octyl) = 1:4.5, PTSA (3.6% of mass of MPA)，water entrainer(17.5% of mass of MPA)， reaction time 8.3 h and the reaction temperature(180-200℃) under nitrogen. The yield is 92.3% and the content of tri-n-octyl maleopimarate ranged up to 99.24% by HPLC. The structure of tri-n-octyl maleopimarate was confirmed by FT-IR and 1HNMR.The acid value，heat weight loss，open-cup flashing point，volume electric resistivity，viscosity and TG-DSC curve of product were measured. In conclusion, tri-n-octyl maleopimarate can satisfy the requirements of plasticizer.