The invention discloses a rosin-base half alicyclic polyamide imide copolymer and a synthetic method thereof. According to the invention, maleopimaric acid dianhydride, 11- amino undecanoic acid and (1, 6) -hexanediamine, which are prepared by taking gum rosin and castor oil as raw materials, are added into stirring polymer reactor together, and the polymer reactor is vacuumized and then fed with inert gases; the polymer reactor is heated hermetically, the stirring rate of the polymer reactor is adjusted, then reactants are thermal insulated and pressurized, and the polymer reactor is released to normal pressure; the polymer reactor is heated once more, the stirring rate of the polymer reactor is adjusted, the polymer reactor is vacuumized continuously after reaching the constant temperature, the reaction is over, and the copolymer is obtained. The synthetic method disclosed by the invention is based on the fusion polymerization principle, and no organic solvent is used during the whole polymerization process, therefore, additional steps for recovering the organic solvent are avoided, and hazards on the human body and the environement are prevented. The polymerized polyamide imide copolymer has good thermal resistance, high-temperature rigidity, size stability and low water absorption, and can be applied to engineering plastics, membrane materials and the like.