In China, reinforced concrete buildings built during the period of the Republic of China have been used for a long time and have various degrees of durability problems. In order to establish scientific standards for preserving such buildings, six typical cases were investigated on site in order to predict the durability and service life of this kind of building. Criteria for calculating the durability and carbonation life of this kind of building were proposed. It is suggested that the service life can be calculated based on the degree of steel bar corrosion and concrete cracking. The projected service lives of these buildings were calculated and analyzed, and the results shows that the remaining service lives of this kind of building are less than 10 years. Therefore this kind of building is in urgent need of strengthening and repair.