Abstract: 3D building models are widely used in geographic information systems, virtual reality, and building information models. Reasonable geometric simplification of the 3D building model can reduce its structural complexity and data size while maintaining the consistency of visual effects, thereby reducing the pressure of graphics rendering and improving the experience of scene interaction. The simplification of 3D building model is one of the hot issues in the field of virtual geographic environment. This paper introduces the problems in 3D building model simplification, analyzes the characteristics of existing simplification methods and classifies them from two perspectives. From the perspective of geometric features, the methods are divided into simplification based on projection features, symbolic expression, and structural features; from the perspective of multi-factor constraints, the methods are divided into simplification under texture constraint, semantic constraint and user's understanding and perception constraint. The advantages and disadvantages of different simplified methods are discussed and summarized. With the goal of building a continuous level of detail model, the development direction of 3D building model simplification research is discussed.