Recently, traditional settlements have become a hotspot in human-nature harmonious coexistence researches. The closure of defensive traditional settlements reflects close human-nature relationships better than average traditional settlements. Although fruitful achievements have been accumulated on defense space, there is no established theoretical system. Systematic literature review and expert interview were used in the research. The current situations concerning traditional settlement defensive space researches as well as related fields, theories, content classification and research methods were collected, organized, summarized and analyzed to provide theoretical references for the preservation and activation of the settlements. A total of 419 screened documents were enrolled for cross-surveillance, reaching the following four conclusions. 1. With the era development, the research on traditional settlement defensive space has shown a rising trend since the 21st century. The researches involve four fields-defensive theories, space types, disciplinary areas and defense types. 2. The domestic defensive theories are under the stage of exploring Western theories. However, local cultures-based theories have not been uniformly summarized. Western theories and domestic cases should be integrated to extract advantages of local cultures and to form a theoretical system. 3. Defensive spaces, which involve 13 key factors (incl. Feng Shui philosophy, landform, image, etc.), are divided in spiritual defense, entity defense and technical defense, and that a system integrating defending objective, defensive space layout and defensive behavior has been formed. 4. Qualitative methods (case study and interview) are the main methods used in the literatures, while measurement, Space Syntax and other quantitative and qualitative methods play an auxiliary role.