The invention provides a biologic polycarbonate and a preparation method thereof. The biologic polycarbonate is obtained by polymerizing biologic epoxy fatty acid ester serving as a raw material and CO2 gas, the yield is more than or equal to 70 percent, the number-average molecular weight is 11,000 to 30,000, and the molecular weight distribution is 1.10 to 1.74; and the biologic epoxy fatty acid ester is obtained by hydrolyzing, freezing and separating unsaturated fatty acid ester from natural vegetable fat and then performing epoxidation, or obtained by direct epoxidation of the natural vegetable fat. The renewable natural vegetable fat and the greenhouse gas CO2 are used as raw materials, so the method is environment-friendly, low in cost and simple and feasible in process operation, the solvent and the catalyst can be efficiently recycled, and the method is environment-friendly and suitable for industrialized production.