Lightweight aggregate concrete is considered as a three-phase composite material composed of matrix cement mortar, intercalated aggregate and interface layer. In line with the homogenization theory in mesoscopic mechanics, the compressive strength of light aggregate concrete is analyzed via numerical simulation. The influences of ratio of aggregate's Young's modulus and mortar matrix's Young's modulus and aggregate's volume fraction on the ratio of concrete's compressive strength to aggregate's compressive strength are examined. Result reveals that there exists a critical value of Young's modulus ratio, below which the compression strength of concrete is dominated by the compressive strength of interface, and above this value the compression strength of concrete is controlled by the compressive strength of aggregate.