Abstract: Diaphragm springs are widely applied in modern vehicle clutches.Because of their particular geometric shape, it is difficult to calculate the characteristics of stressdeformation of the springs. The Almen-Laszo formula, deduced from disk spring model are still used to estimate the stress of diaphragm spring. In engineering the most fatigue crack origins emerge nearby inner edge of the springs, but the analyzed results of the Almen-Laszo formula fail to explain this phenomenon. In this paper，the stressdeformation characteristics at fatigue crack origin of diaphragm spring of three different types are measured with strain gauges. A comparison between the test results and calculation with the Almen-Laszo formula was done. It is found that at the maximum working deformation, the values of test stress are 20% larger than that of calculation with the Almen-Laszo formula. A modificative calculation method to the Almen-Laszo formula was proposed. Linear correlation between the modification coefficients and the notch width was also found. The results of modificative calculations of the parts are well coincided not only with ones of test samples but also with spring used in vehicle CA630. 