Abstract: This paper involves the introduction of the Groundwater Hydrochemistry Assistant Analysis System and its application in the Ordos Basin.According to Component Object Model(COM)technology and secondary development of C# language,the system is designed based on MAPGIS 65.The system can implement not only basic database management,figure display and query but also perform isoline drowing.It can draw the contour map of the total dissolved solids(TDS)and anion concentrations and cation concentrations.It can also carry out superposing analysis function to draw the map of hydrochemical types.Moreover,the system of the secondary development has function that stores ultimate figures into the spatial database.It is not steady but flexible at any moment.It can discretionarily superpose other figure layers that forms synthesis figures.The multi-layer maps can supply accessorial support for the study of zones of hydrochemical types and occurrence of groundwater hydrochemistry.The Ordos Basin covers parts of Shaanxi,Gansu,Shanxi,Ningxia and Inner Mongolia.The basin lacks significant surface water resources and the groundwater quality is poor.Among the water-bearing formations,the Luohe formation has the most extensive distribution which can produce the most groundwater.The groundwater quality of the Luohe formation is very complex.Exemplifying the study of the hydrochemistry type of groundwater in the Luohe formation and performing validation in practice,the system is practical and valuable.As a result,the distribution of hydrochemical types in groundwater in the Luohe formation is consistent with the hydrodynamic field.The system is useful to study the recharge,runoff,and discharge conditions of the groundwater and also useful to evaluate sustainable utilization of groundwater resources in the Ordos Basin.