The invention relates to a furan dioctyl phthalate-lactic acid-dihydric alcohol copolymer and a preparation method thereof. The preparation method comprises the following steps: firstly, preparing oligolactic acid in a lactic acid polymerization mode, subsequently preparing furan dioctyl phthalate dihydric alcohol ester by using furan dioctyl phthalate and dihydric alcohol, and finally copolymerizing the oligolactic acid with the furan dioctyl phthalate dihydric alcohol ester, thereby obtaining a target product, namely, the furan dioctyl phthalate-lactic acid-dihydric alcohol copolymer. The vitrification temperature of the copolymer of the series is 10-90 DEG C, and the weight-average molecular weight is 5000-150000. The copolymer prepared by using the method can be completely degraded, is good in thermal property and mechanical property, and has good application prospect in the fields of degradable plastics, degradable fibers, agricultural plastic mulching films, controlled-released medicine carriers and the like.