Abstract: This paper has derived a new method to calculate the critical temperature T_K, which, as the temperature increases, is yielded by the thermobending phenomena in the round-longer bar under four different conditions of binding, i.e. both ends hinged, both ends fixed, one end fixed whereas the other hinged, and one end fixed whereas the other free. The collocation method of MWR(Method of Weighted Residuals ) is used to analyse and calculate in this method, with which the common formula.