The invention relates to the field of functional macromolecular materials, in particular to novel linear temperature-sensitive type polyurethane and a preparation method thereof. The preparation method of polyurethane comprises steps as follows: polycarbonate diol and dimethylolpropionic acid are added to an organic solvent and are mixed uniformly at the temperature of 75-85 DEG C under the protection of nitrogen, then hexamethylene diisocyanate and a catalyst are added, the mixture is stirred at the temperature of 75-85 DEG C and reacts for more than 3 h to generate linear polyurethane with isocyanato as an end group, ethylenediamine and triethylamine are added, the mixture is stirred to react for 2 h or longer, linear polyurethane with amino as an end group is obtained, N-isopropyl acrylamide is added, the mixture is stirred to react for 12 h or longer, then deionized water is added, an organic solvent is removed through rotary evaporation in a vacuum state, and the novel linear temperature-sensitive type polyurethane is obtained. Two ends of a polyurethane chain segment of the novel linear temperature-sensitive type polyurethane are directly sealed with N-isopropyl acrylamide, no other chain segments are contained, the synthetic method is simple, the synthesis and chemical grafting steps of poly(N-isopropyl acrylamide) are omitted, synthetic raw materials are also saved, and the cost is reduced.