The Ordos Cretaceous Basin is located at western area, a arid-semiarid area. Its south section and north section is covered by loess and desert, respectively. Chemical compositions of groundwater are prominently different regionally. In the north, freshwater dominates the groundwater, but in the south, brackish water does. 8 groups of hydrochemical and isotopic samples were collected from deep groundwater (more than 400 m depth) in this basin. Results of T and 14C show that groundwater residence times are within 20343 years, and are not polluted by human being. Based on Cl concentrations and 36Cl of groundwater, influences of evaporation on the recharge of precipitation and the Cl concentrations of groundwater were discussed. This study shows that all of the evaporation and the dissolution of stratum Cl have magnitude effects on the Cl concentrations of groundwater. The groundwater in the desert section was evaporated by 29.9-63.0 times in comparison with precipitation during its recharge, which provided more than 21.3-45.3 mg/L of Cl to the groundwater. In the loess section, the groundwater was evaporated by 266.0-523.7 times, with 191.5-377.0 mg/L of Cl derived from evaporation.