Since the 1980s, the distributed optical fiber temperature measurement technology has gradually carried out to be the long-distance, high-precision and long-time temperature measurement, and is more and more used in many fields such as fire warning, leakage monitoring, etc. Since the 21st century, scholars in the field of hydrogeology have used this technology to understand the heat transfer in groundwater, surface water and other media. In this study, the distributed optical fiber temperature measurement technology was used to measure the vertical temperature of groundwater in the downstream of Huangbizhuang Reservoir in North China Plain for 35 sites, and groundwater table has been measured too. On the base of the temperature data, the plane and vertical distribution of the groundwater temperature are obtained. The plane distribution of the groundwater temperature shows that the reservoir water of Huangbizhuang Reservoir recharges the groundwater in the downstream plain area through the seepage at the bottom of the auxiliary dam, and the isotherm is roughly parallel to the groundwater contour, which shows that the conclusion of this technology is reliable. And according to the vertical temperature distribution, the main recharge depth is about 23 and 28 m underground. And the points of seepage are indicated by temperature change inside the dam and the drainage ditch.