Abstract Building green retrofit is considered as an effective means of energy saving and achieving sustainable development goals. The success of a building retrofit is highly dependent on the retrofit strategies used. However, it remains challenging to select appropriate retrofit strategies for a specific retrofit building. There are numerous cases of building retrofit around the world, which can be collected, stored, and analysed. The knowledge gained from these cases could provide a useful reference for making decisions on new retrofitting projects. This study presents a case-based reasoning (CBR) approach to support building green retrofit decisions. A total of 71 retrofit cases in China were collected. The attributes of the retrofitting buildings were identified, including the general building information, component information, and energy and cost information. A synthetic optimisation weighting method was adopted based on both expert opinion and the attribute characteristics. A real retrofit case located in Shanghai was used as a case study to demonstrate the application of the CBR approach. The results indicate that the CBR approach can aid in identifying similar cases from the case database, and extracting valuable information from these. The experience and lessons learned from past cases can guide decision makers in making improved decisions on new green retrofit projects.