Abstract: The rigid polyurethane foam blown by water was prepared with a polyisocyanate polyaddition (PIPA) polyol synthesized in lab and a polyol with a low hydroxyl value. The effects of such factors as the ratio of two polyols，chain extender and cross linker，isocyanate index on polyurethane product mechanical properties like compression，bend，impact strengths and dynamic rheological properties were studied. When the ratios of 1，4-butanediol，trimethylolpropane and TMN-3050 were 1.0pphp，1.0pphp，15pphp respectively，and the isocyanate index was 1.15，the product performed best with good strength and toughness.