Abstract: The products of the square - root of internal pressure A and the molar volume of the repeated unit Vm for various polymeric liquids at 298.15 K are plotted against their van der Waals volumes . A straight line through the origin of coordinates is obtained. This means that the A Vm of polymers has good group additivity . Therefore, a method of group contribution which can be used to predict the internal pressure of polymeric liquids is established. Combining with Small’s molar- attraction constants , the values of new solubility parameter defined by the authors’ previous work for various polymers at 298.15 K can be obtained from this method.