Using Kelvins equation and the Clausius Clapeyron equation, vapor and liquid flows through porous building materials may be expressed as a unified functions using water vapor partial pressure as driving potentials. Mathematical model of coupled heat and moisture transfer for multilayer wall was established and validated using temperature and water vapor partial pressure as driving potential. The temperature and moisture variations in 10 years aerated concrete masonry wall were simulated according to the typical meteorological data of Shanghai. With original condition that the temperature was 298K, the mass moisture contents were 291%, 345%, 503%, 860% for four different construction conditions respectively, temperature and moisture distribution in wall was independent of original condition after one year of use. In phase of the normal use condition, the relative humidity inside wall was less than 10 without condensation occurring, but in some time period the relative humidity was higher than 08 causing mildew generation. Moisture content inside wall changed periodically, varying between 334%831% with an average of 445% in air conditioning season, 331%369% with an average of 347% in heating season.