Abstract: In order to discuss the mechanical properties and fracture characteristics of dam concrete, a three-point bending test of concrete beam was carried out based on two different concrete mix ratios (named C_0.48 and C_0.43 respectively according to different moisture contents) provided by a hydraulic complex project and on-site coarse and fine aggregates. The relevant mechanical properties such as slump, compressive strength and splitting strength were determined, and the effects of different mixing ratios on fracture parameters such as fracture surface, cracking load and instability load, critical effective crack length and double K fracture toughness were analyzed. The test results show that the collapse of C_0.48 concrete is greater than that of C_0.43 concrete. The compressive strength and splitting strength of C_0.48 concrete are lower than those of C_0.43 concrete. The coarse aggregate of C_0.48 concrete fracture surface is not as obvious as that of C_0.43 concrete. The cracking load, destabilization load, critical effective crack length and fracture toughness of C_0.43 concrete are higher than those of C_0.48 concrete, which indicates that C_0.43 concrete has high strength, good ductility and good toughness.