The invention discloses a resource reuse method and a resource reuse system for improving the energy efficiency of a D2D (device-to-device) system. The method comprises the following steps that 1, the position estimation is carried out on the emitting end and the receiving end of D2D user pairs, and the position information is obtained; 2, whether the distance from the sending end to the receiving end is greater than the threshold value or not is judged according to the position information, when the distance is greater than the threshold value, the current timeslot idle cellular users are selected to be used as a relay node, in addition, the operation enters the third step, and otherwise, the operation directly enters the third step; 3, the cellular users with resources distributed by a base station and each group of D2D users are respectively combined, and an energy efficiency matrix and a velocity matrix are built; 4, the resource reuse decision making is carried out on the basis of the preset criterion, and the channel reuse matrix is obtained through solving; 5, the reuse cellular users of each group of D2D user pairs and the corresponding optimum emitting velocity are determined. The resource reuse can be carried out at the same time as the expenditure reduction realization only according to the position information of users in a cell, and the total energy efficiency of a communication system is improved.