Abstract: This paper considers that the methods of aerial photogrammetry and three-dimensional basic geology mapping are suitable for detecting the lateral mountain space while the technique methods of engineering geological drilling, monitoring while drilling and geophysical well logging of multi-parameters can be used in detection of vertical underground in loess hilly and gully region like Yan'an, among which the detection effect of engineering geological drilling and geophysical well logging of multi-parameters is much better. The detection result shows that the rock and soil of underground in Yan'an center areas can be divided into 8 soil mass mapping units and 5 rock mass mapping units, and the quartz sandstone strata of Baotashan Member in Middle Jurassic Yan'an Formation is favorable for underground space exploitation. It concludes four types of underground geological structure in Yan'an City, i.e. the loess gully region and slope zone of lateral mountain space geological structures, and the valley terrace area and the excavation and filling area of human engineering activities in vertical underground geological structure. The research result can provide controlled and accurate data for the establishment of a three-dimensional geological structure models in the area.