Abstract: The effect of packing coefficient E,isocyanante index and temperature on mechanical properties of water blown rigid polyurethane foams with constant density about 350 kg/m³ have been investigated.It is shown that compressive strength increases with the increase of packing coefficient E,isocyanante index and temperature,while bending strength shows different trends with different variables.Scanning electron microscope (SEM) has been used to observe the foams cellular microstructures,whose result indicates that the average cell diameter decreases from 188 μm to 151μm with the packing coefficient E increasing from 2 to 3.