Abstract: A simplified method for determining the initial fracture toughness of dam concrete was examined in this study based on the linear regression theory. It determines initial cracking load using a P-Δ curve of load versus crack opening displacement, which is linear before cracking and takes a sudden drop in linear correlation coefficient at cracking stage. It was verified using previously reported experimental data on dam concrete of wedge-splitting specimens with aggregate sizes up to 150 mm and three-point bending specimens with aggregate sizes up to 80 and 40 mm, respectively. The new method has a higher accuracy and avoids use of strain gauges for measuring initial cracking load in the traditional method. Thus, relative to other analytical methods, it is easier to operate without complicated calculations and insensitive to artificial factors. Moreover, the method was used to examine the effect of specimen sizes on initial fracture toughness, showing its insignificance in application.