Polyurethane elastomer (PUE) is generally composed of soft and hard segments. The soft segment is usually a single polyol structure, and the hard segment is formed from the reaction of isocyanate and chain extender. If two kinds of polyols with obviously different structures are used, triblock cross PUE with two soft segment structures can be prepared. Polyurethane prepolymers were synthesized by the reaction of hydroxyl polybutadiene (HTPB) and polyoxypropylene glycol (PPG) with toluene diisocyanate (TDI), respectively. The two prepolymers were mixed according to the ratio and then expanded by 1,4-cyclohexanedimethanol (CHDM) to prepare a series of triblock cross PUEs. The structural, mechanical and thermal properties of PUE were characterized.The results showed that when the total content of soft segments containing PPG and HTPB in PUEs was among 54.2%~55.4%, the proportion of HTPB in soft segments had great influences on the mechanical properties and microstructure of PUEs. With the increase of the proportion of HTPB segment in the soft segments, the hardness, specific strength and elongation at break of PUEs first increased and then decreased. When the proportion of HTPB in the soft segment was 20.18%, the specific strength, the elongation at break,and the hardness of PUE reached 18.44 MPa/(g/cm³), 404.6% and 32 Shore D, respectively.