Abstract: This paper analyzes the size effect of the fracture parameters of low-heat cement fully-graded concrete. Wedge-splitting specimens with effective heights of 0.75 m, 1.5 m, and 2.25 m were cast on the construction site of a dam project, and tests were carried out to obtain the stable double-K fracture parameters of low-heat cement fully-graded concrete. Based on the test results, theoretical methods were used to derive the size independent unstable and initiation toughness of fully-graded concrete, and to predict the maximum and initiation horizontal loads of a specimen with an arbitrary dimension. The study found that when the ratio of ligament height to the maximum aggregate dimension is greater than or equal to 6.0, the double-K fracture parameters tend to be stable. The size effect model and its evolution forms can be used to determine the size independent unstable and initiation toughness of fully-graded concrete, quantitatively to analyze the influence of strength and toughness on crack propagation, and by introducing an equivalent geometric parameter, the prediction equations for the maximum load and crack initiation horizontal load of arbitrary size specimens can be established respectively.