Abstract: Meso-mechanics method of composite materials is adopted to analyze the mechanical properties of concrete in moisture conditions, which are influenced by the different volume fraction ratio of kinds of phases, pore rate and also the water saturation. Cement-based concrete can be defined as a combination of four phases: coarse aggregate, hydrated mortar, active pore and entrained non-active pore; the active pore will be filled with free water in moisture environment. Two types of pore and the mortar are regarded as the equivalent matrix, and the aggregate as the inhomogeneous inclusion. A kind of double inclusion model is proposed based on the equivalent inclusion theory and the Mori-Tanaka’s concept of average fields. A united compressive strength expression is established by combining with the fracture mechanics method. The influence of various factors on the compression strength can be reflected by parameter analysis. The theoretical results demonstrated that the strength of concrete is controlled by the weaker component between the aggregate and mortar, that existence of pore water would, compared with the dry concrete, lead decrease of compression strength of wet concrete, which are agreeable with the experimental results.