Abstract: A simplified extreme method and corresponding model are developed for determining the initiation toughness of dam concrete. Based on the extreme method, we derive an analytical expression for the initiation toughness of wedge splitting specimens and a simplified extreme method for determining the initiation toughness of dam concrete. This simplified method needs only the peak load data measured in fracture tests and can avoid the shortcomings of the traditional test that requires measurements of critical crack opening displacement and initial load by pasting strain gauge and complicated numerical integration. We test it in application to calculating the initiation toughness of dam concrete specimens with different sizes and ages, examine the accuracy of calculations in the condition of different crack opening forms, and compare the calculated values with those by traditional methods. The results show that no obvious effect on the calculated initiation toughness has been found in this study when using different crack opening forms. Even using the simplest linear formula, our simplified model can give an accurate calculation of initiation toughness, and the calculations are in good agreement with previous experimental measurements in strain tests and calculation results using linear regression method, thereby verifying the method and model developed in this study.