Abstract: Taking for example the modifcation of the. 1: 50,000 Geological Map of Huangznuguan Sheet of Chengxian County, Gansu province, this paper discusses the important role of the application of modern sedimentology, improvement of the theory of stra- igraphy and study of petrostratgraphy in regional geological surveys. 1. The petrological and sedimentary characteristics and sequence of strata and the shape of a stratigraphic body are conditions of prime importance for recognition of anobjeective petrostratigraphic body, which is elucidated with reference of the examples of the Bijiashan limestone and the Wangjiashan Formation. 2. The sediment in the sheet area are dominated by Devonian strata. According to the fact that the accumulation of the sediments was obviously constrained by the sedimentary basin, the author used the method of establishing the petro-stratigraphic sequences with the basins as the units and reconstructed the real ancient framework of distrbution of Devonian sediments in the study area. 3. There are appreciable differences between the Huangzhuguan Sheet modified by using reestablished stratigraphic units and previous geological map. The structure of the map face not only reflects the spatial distrbution of the petro-stratigraphic body, but the combined stratigraphic units can also be used to mark the sedimentary basins and paleogeographic environments and infer the sites of possible accumulation of sediments and their influence on the structural analysis. Therefore the modified Huangzhuguan Sheet has a function that cannot be replaced by previous maps in the analyses of regional stratigraphy, regional structure and geological history.