Energy saving of buildings, which is directly related to national energy strategy, environmental protection, and sustainable development, is an important research topic. Energy-saving of external walls is the important research content of building energy-saving technology. Energy-saving technology on external walls mainly includes external thermal insulation technology of exterior walls, thermal insulation technology of inner walls, and self-insulation technology. The importance of thermal-insulating and energy-saving is analyzed and the main characteristics of two kinds of heat preservation technologies are discussed. Research advances in China are systematically introduced. And the considerations involving the insulation technology of building external walls are put forward.