A method which allows for the random structure of aggregates in the numerical simulation of fully graded concrete at a mesoscopic level was developed. Two dimensional geometrical model and the finite element model were automatically generated by coupling the commercial software COMSOL with MATLAB. The generation process was based upon the proposed numerical image processing technology and the different interfacial embedding criterions wherein the aggregate particles were generated from a certain aggregate size distribution and then placed into the concrete specimen in such a way that there was no intersection between the particles. The effectiveness of the proposed method had been assessed by simulating four kinds of coarse aggregate shapes. It is shown that a high efficiency can be achieved in placing aggregates and automatic meshing preprocess for high volume fractions of aggregates in fully graded concrete.