In this study, a new convenient method for the determination of the interfacial tension between two immiscible polymers in melted state is proposed. For an extended thread in a liquid matrix, it is difficult to get a regular sinusoidal disturbance in some systems. But after a liquid thread in matrix breaks up, we can see a process of ellipsoidal drop retraction. By directly using this process, we can measure interfacial tension of polymer melts avoiding the Limit of the breaking thread method. The new method is much easier when compared to traditional drop retraction methods. We use a second rank tensor S to describe the shape evolution instead of the deformation parameter D in Taylor's theory. Analysis of this interfacial tension driven process leads to a theoretical relation between the shape retraction rate, the three semi-axis of ellipsoidal drop and rheological characteristics. The interfacial tensions determined by the method are in good agreement with those data given in the literatures for systems with either high or low viscosity ratio.