Building energy efficiency is an important field in energy efficiency. In China, building energy efficiency, as an important link in realizing the country’s energy strategy, has been listed by the National Development and Reform committee in the 11th “Five Year Plan” as one of the ten key energy efficiency projects. Building energy efficiency belongs to the field where the market mechanism doesn’t work and it should be guided and adjusted by the government’s policy, which demands strong support from laws and regulations. Yet, the legal system concerning the building energy efficiency is not complete, which has become an important factor that limits the development of building energy efficiency. The paper analyzes China’s existing legal system of building energy efficiency and points out specific problems and incomplete places with it. Aiming at the needs of building energy efficiency at present in China, the paper points out that the legal system of building energy efficiency can be perfected from four aspects: The fundamental law in energy efficiency, “Energy Efficiency Law”, the primary law in the building industry, “Construction Law”, the administrative regulation, “Administrative Ordinances for Building Energy Efficiency” and the departmental regulation, “Administrative Regulations for Civil Building Energy Efficiency”. The paper puts forward suggestions of modifying, establishing, or revising the four legal documents and bringing them into agreement and thus providing practical legal support for carrying out the work of building energy efficiency in China.