On June 23, 2000, the water color of Long-07^# observation well in Qingshui county, Gansu province,changed from achromatic to blue suddenly. Using the data of all-around water quality analysis, the hydrogeochemical process and mechanism of the event are studied, and the relation between tectonist activity in margin area of Qinghai--Tibet plateau and the water color changing event before west to Kunlun Mountain Pass Ms 8.1 earthquake is discussed,combining with other anomolies in eastern Gansu province.