Abstract: The groundwater from Qinling tunnel on Xi’an-Ankang railway is drained into two rivers-the south into Taiyu river, and the north into Shibianyu river. In order to evaluate the influence of chemical abnormal quality the drained groundwater, the water quality of the two rivers is observed and tested in three sections respectively for three times between 1998 and 1999. Some evaluation factors of the criteria for drinkable water are adopted to divide the surface water into three levels in quality. Fuzzy comprehensive evaluation method and gray system method are used to comprehensively evaluate the quality of surface water in the three sections. The results show that the water quality in the two rivers are not influenced by the tunnel construction and by the water drained from the tunnel.