Deep-borehole heat exchangers (DBHE) is currently recognized as the most environmentally friendly way to exploit geothermal energy. The deep coaxial borehole heat exchanger is the most common type of DBHE. Heat extraction capacity and influence radius are the controversial problems in the process of popularizing this technology. Based on the measured parameters of ground temperature and thermophysical properties, the heat extraction capacity and influence radius of the 2 500 m deep coaxial borehole heat exchanger were analyzed by the way of in-situ test and numerical simulation in Caotan area of Xi'an. The results show that the sustainable heat extraction power of the heat exchange well in 30 years can reach 350 kW, with an average linear meter of 140 W. The attenuation degree and range of wall rock temperature increase with the increase of heat extraction power. The influence radius of the deep coaxial borehole heat exchanger are different at different depths, and the deep stratum is larger than the shallow stratum as a whole. The influence radius of the 2 500 m deep coaxial borehole heat exchanger with the heat extraction rates of 140 W/m can reach 110 m after work for 30 years.