With China's urbanization speeding up, increasing urban construction such as city water supply, utilization of underground space resources, ground improvement, garbage disposal are closely related to geological work. Especially, metropolitan cities building on the Quaternary are being threatened from earthquake, active faulting, land subsidence, water shortage, scarce land, environmental deterioration, etc. Beijing, as one of the few gigantic metropolitan cities around the world, has no exception. But the subsistence and development of these cities are indispensable to the Quaternary unconsolidated sediments. Therefore, it is essential to understand the 3D geologic structures of the Quaternary, because it will provide detailed spatial distribution data of geological bodies so as to prevent and reduce the occurrences of abovementioned disasters. This study based on the distribution, type and features of the Beijing Quaternary plain put forward an approach to establish the 3D geological structural model, upon which the 3D digital model of geological bodies in the piedmont plain in Beijing was established. This provides a new mean for conducting geological investigation on the Quaternary and achieved a satisfactory application result.