In order to essentially improve interfacial transition zone between cement paste and aggregate, the concept and ideal model of function aggregate are developed. Function aggregate is composed of a porous matrix with high strength and low water absorption, and a coating layer which can hydrate in cement paste. It can improve ITZ between aggregate and cement paste and control curing range of cement paste. Based on optimization of raw materials and processing techniques, high strength aggregate with low absorption and minor C2S and C4AF phase in coating layer is acquired. Results indicate that cordierite is formed in aggregate when MgO content reaches 2%, and it shows that the presence of cordierite minimizes the potential for micro-crack formation, thus decreases water absorption.