Aerated concrete(AC) was prepared by the non autoclaving method, and micro encapsulated phase change materials(MPCMs) were added during the preparation process to obtain MPCM/AC phase change composite materials and RT25 paraffin was selected as the phase change material(PCM). The specific heat capacity of the composite samples was measured at both 17，40℃, while the paraffin was in solid and liquid phases, respectively. Dependence of the MPCMs loading and the effective thermal conductivity were also investigated. Furthermore, the heat storage coefficients of the composite materials were derived from the above parameters to evaluate the thermal performance of composite materials. Results show that both the effective thermal conductivities and specific heat capacities increase upon adding the micro encapsulated paraffin. However, they are found to decrease at further increase of the paraffin loading. The w(MPCMs)=1.0% composite materials samples are found to have the best heat storage performance, its coefficient of heat accumulation reaches 335W/(m2·K), better than the control group by 74%.