Optimizing the built environment is an important strategy to prevent obesity and improve health level of the population. Density is the most common factor among built environment elements and the relationship between it and obesity has attracted much attention in recent years. However, given that research on the relationship between density and obesity has just started in China, this relationship is not yet clear. If density planning measures are blindly adopted, it might directly affect the effectiveness of healthy city planning and be detrimental to the promotion of the Healthy China Strategy. Therefore, it is urgent to clarify the relationship between density and obesity in order to enrich the relevant theories of urban and rural planning and urban geography in China and provide theoretical support for the construction of healthy cities. For this reason, based on the systematic review approach, this article reviews the relationship between population density and obesity from the aspects of research areas, publication time and quantity, variable selections, research designs, model settings, empirical results, etc. After fully grasping the current research status, this review finds a potential U-shaped relationship between density and obesity, and proposes that future research should strengthen attention to the Chinese context, identification of causal relationships, and comprehensive measurement of density and obesity and other important issues.