Abstract: The macroscopic mechanical properties of concrete are highly related to its internal mesoscopic composition. This paper presents a theoretical prediction model of concrete macroscopic mechanical properties considering the mesoscopic composition. Firstly, the parameters in the theoretical model are calibrated by meso-scale numerical tests. Then, the size effect of the concrete fracture energy and the uniaxial tensile strength in material-level is analyzed based on the proposed model. The results show that the concrete fracture energy and the uniaxial tensile strength both vary with the aggregate gradation (i.e. the maximum aggregate size), and they are also influenced by the characteristics of aggregate-matrix interface. When the aggregate-matrix interfaces are weak, the concrete strength is low, and the concrete fracture energy and the uniaxial tensile strength both decrease with the increase of the aggregate gradation. When the aggregate-matrix interfaces are relatively strong, the concrete strength is high, and the concrete fracture energy and the uniaxial tensile strength both increase with the increase of the aggregate gradation. The calculation results are in good agreement with the test results and verify the accuracy and rationality of the theoretical prediction model established in this paper.