In order to probe the function of the small courtyard during fire, studies and fire tests in a real dwelling building and an analog building with a small courtyard have been carried out in China. The preliminary conclusions are: 1. The small courtyard in dwelling building can play a valuable part in ventilating smoke and heat. When the building is on fire, the small courtyard will be helpful to evacuating residents and extinguishing fire by fire-fighters. 2. The horizontal distance between any two windows in the courtyard should not be less than 3.3 meters. The paper provides theoretically the detailed analysis of the above conclusions and test data in many aspects. These data have been provided as a valuable reference for the Code of Fire-Prevention in Building Design.