Abstract: Proposes an age-dependent size effect fracture model for concrete. Based on the existing models, an evolution form of the size effect model is established to determine the fracture failure of concrete specimens with variable sizes and ratios of crack to height. Combined with the time-varying characteristics of model parameters, a size effect fracture model considering the age effect is proposed. The applicability of the model is verified by the concrete fracture test results in the literature with different specimen ages, sizes and ratios of crack to height. In order to ensure the accuracy of the model predictions of concrete fracture failure at a specific age, it is recommended that the material constants used in the model should be determined from fracture test results of at least 3 groups of concrete specimens, with the ratio of maximum to minimum equivalent crack length not less than 4. The exponential function form can well describe the time-varying characteristics of concrete material constants. The age-dependent size effect model can accurately predict the fracture failure of concrete members with variable ages, sizes and ratios of crack to height.