Abstract: The development of underground space has gone towards deep earth in Beijing City. The importance of the study on Tertiary engineering geology is increasing prominently. The Tertiary engineering geology is weak in contrast to the Quaternary engineering geology in Beijing.Based on the analysis of abundant engineering geological data and according to the general theory of sediment, the Tertiary sediment is discussed systematically from the point of geological structure for the first time. A series of conclusions are deduced. On the basis of the data of borehole and physical mechanical test, the unified engineering geological stratum is further discussed. It is an important support for the planning of the deep underground space in the Center region (with the depth of 100m and area of 336km2) of Beijing City. At the same time, it serves good references for further study on the Tertiary geology, especially Tertiary engineering geology from methodology and idea.