Abstract: In this paper we systematically discussed the basic circumstance and the ambient hydrogeological environment of the hot well in Zhangdaokou observatory,and provided the date of water temperature observed at depth of 105-195m.We analyzed why low temperature anomaly occurred at depth of 165-185m which departs from normal geothermal increasing,and point out that about 220m is the best geothermal observational layer.This study can be used as reference for the selection and construction of national geothermal observation networks.