The invention discloses a polyurethane containing a plant oil structure in a soft segment in multi-block polyurethane, especially containing three tung oil conjugated double bond structures in the soft segment, and a synthetic method thereof, and belongs to the field of polymer synthesis. The polyurethane provided by the invention is characterized in that a pre-polymerization method is adopted, tung oil-caprolactone polyol containing three conjugated double bonds in a side chain reacts with diisocyanate and a diamine or glycol chain extender so that polycaprolactone containing a plant oil structure in the side chain, in particular a polyurethane multi-block copolymer containing tung oil derived conjugated double bonds, is obtained. The new polycaprolactone type polyurethane containing the tung oil conjugated double bonds has the comprehensive excellent properties of both of the polycaprolactone type polyurethane and the plant oil, and also has the advantages of good glossiness, high drying speed, waterproofness, solvent resistance, good thermal stability and the like, so that the polyurethane is a new plant oil-based polyurethane.