Abstract: Brackish groundwater is one of the important water resources in arid and semiarid areas. During the period from September to October 2011, 71 groundwater samples were collected in the irrigated area dowstream from the Hongyashan Reservoir in Minqin County, Gansu Province, and the traditional statistical methods and geographic information software were used to research the spatial distribution of brackish groundwater in the Minqin Oasis. The result showed that brackish groundwater (＞1 g•L-1) in the Minqin Oasis was distributed in an area of 781.59 km2, in which the proportion of areas with brackish groundwater (1-3 g•L-1) was 27.6%, and these areas were distributed in Quanshan District and some parts of south Lake District. The proportions of areas with salt water (3-10 g•L-1) and brine (10-50 g•L-1) accounted for 55% and 17.4% respectively, and these areas were mainly located in Lake District. With increasing groundwater salinity, the chemical type of brackish groundwater changed gradually from SO2-4-Cl--Mg2+-Ca2+ (brackish groundwater) in Quanshan District to SO2-4-Cl--Mg2+-Na+ (K+) (brine) in Lake District. Climatic and geological conditions and human activities were the main factors of forming brackish groundwater.

Key words: brackish groundwater, spatial distribution, formation cause, development trend, Minqin Oasis