This paper presented a novel polyurethane based on uniform-size hard segments. The prepolymers of poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) (PLA-PEG-PLA) were synthesized via bulk ring-opening polymerization with PEG (Mn=600,1000) as initiator and L-lactide as monomer. The chains of prepolymers were extended with diurethane diisocyanates based on inexpensive 1,6-hexanediisocyanate to give the aliphatic polyurethane (PU-I, PU-II), and as a control, the aromatic polyurethane (PU-III) was prepared with 4,4’-diphenylmethane diisocyanates (MDI) as chain extender. The chemical structures of diurethane diisocyanates, prepolymer and PU were confirmed by NMR, FT-IR, HR-MS and GPC. The effect of uniform-sized hard segments on the properties was studied by researching the thermal properties, mechanical properties and in vitro degradation properties of PU films. Comparing with PU-III, PU-I has better mechanical properties (ultimate stress of 21 MPa, elongation at break of 840%) and faster degradation rate (19 d). Comparing with PU-I, the PU-II containing more PEG in the main chain shows lower ultimate stress, higher elongation at break and faster degradation rate. The non-toxic degradation products, suitable mechanical properties and degradation rate of this kind of polyurethane can make them substitutes for MDI-based polyurethanes and use for further biomedical application.