Abstract: The TPB specimen was used in the experiment. The Δa_i of every unloading points was were determined by means of the unloadingcompliance curve LEBC=f((△a)/(ω-a₀)) of a post-yeild spedimen. Meanwhie, the J-R curve was determined. A new approach to get the crack initiation point has been introduced by using the second of inflexion on the V_g-△ curve. The new results were obtined from the new approach. As compared with the multispecimen methnd, this method is much betler withe erors being less than 10 per cent.