Groundwater is very important water source for the survival and development of oasis in arid area. The hydrochemical data of 66 groundwater samples in Yaoba Oasis of Inner Mongolia were selected to analyze the hydrochemical characteristics and genesis of groundwater with methods of classical statistics,Piper trigraph,Gibbs graph,main ion concentration graph,etc to understand the chemical characteristics and causes of groundwater,and also to provide the basis of data for water quality evaluation. Results showed that the groundwater presented weak alkalinity and brackish water. The main chemical processes were evaporation concentration and rock weathering. The main sources of groundwater chemical components were dissolution and precipitation of calcite,dolomite,rock salt and gypsum. From northeast to southwest,the chemical types of groundwater changed from SO4·ClCa·Mg and SO4·HCO3·ClMg·Na to SO4·ClCa·Na. The high salt ions were enriched. The overall salinization degree of the groundwater body is obvious. It will provide guidance for rational exploitation and protection of groundwater in this area.