The evolution of confined groundwater chemical type from upstream to downstream is SO4·HCO3-Na→SO4-Na·Ca→SO4·Cl-Na·Ca→SO4·Cl-Na or SO4-Na·Ca, which has the hydrogeochemical zonality. The water-rock interaction simulation has been applied by method of reverse simulation in PHREEQC software to study its mechanism.The simulation results indicate that the process of confined groundwater evolution from upstream to downstream mainly contains the dissolution of gypsum and halite, the sediment of Ca-montmorillonite and niter. The dissolution/ precipitation amount of minerals in groundwater increases gently in study area from upstream to downstream.The water-rock interaction gradually increases. It got the two conclusions that the dissolution/ precipitation of minerals and positive ion exchange control the evolution,the reason that the water-rock interaction strengthens from upstream to downstream area is that the particles of water-bearing medium becomes fine gradually.