Abstract: The mechanism of transmit heat and the calculation model of the thermal conductivity of the soft polyurethane foam have been discussed and the affect factors of the thermal conductivity.Temperature,density,and squeeze,absorb water the rate,environment pressure etc,have been analyzed.On these influence of affect factors of thermal conductivity,the thermal conductivity of the soft polyurethane foam has been measured and the relation curve of thermal conductivity have been given.On the basis of the measured,the general relations of thermal conductivity of the soft polyurethane foam have been setup.The reference of design for the application of theramal insulation has been provided.