In this study, we devised a downhole heat exchanger with multi-pipes of a new type unlike the conventional method, and we considered the heat extraction performance of this method by numerical calculation. We found that the heat extraction rate increases although the temperature of the flowing heat extraction media in the heat exchanger falls with increasing gross flow rate of heat extraction media. In addition, the heat extraction rate of the heat exchanger with multi-pipes is larger than the heat extraction rate of a triple u-tube heat exchanger.