On the basis of the drilling data of 16 wells, the 2D profiles of the seismic characteristic parameters (e.g. velocity) were built for a total of 5000 km seismic sections by applying a comprehensive calibration on these seismic data. Furthermore, using the variable velocity mapping method, the isopach map of the saliferous strata of the M56 stage, which are the main potash rich strata in the Ordovician northern Shaanxi salt basin, was preliminarily obtained, and the tectonic differentiation in this region was also discussed. In the M56 stage of Ordovician, the northern Shaanxi salt basin shows the tectonic pattern of “two depressions and one lifting”, and there are five salt sags with the thickness of more than 150 meters in this region. In this study, we found that the western salt sags showing NNE spreading are controlled by the syndepositonal faults in the west of the basin, and the east two salt sags is divided into two salt sub-swamps (the east and the west). All these observations above indicate that there exists many relatively active salt sub-sags that controlled by the syndepositonal faulting in the inner northern Shaanxi salt basin. These salt sags are good for gathering potassium materials, and provides enough accommodation space for the large marine potash formation. And more drilling works are needed to get further understanding.