Abstract: Based on the analysis to the abrupt change in hydrochemical observations of the well located in the yard of Zhengzhou Seismological Bureau and some test of water pumping, the affection of pumping time to the observation is studied.The results showed that the pumping time influenced the observations greatly, which obeys the relation y=ae^b/x, especially when pumping lasted 2~3 hours, the variation was the largest, then a little undulation round the abnormal value.Thus, the abrupt change in each hydrochemical observation item was cased by water pumping, not seismic anomaly.