Using the CLT code, the resistivity dependence of the reconnection rate during the explosive phase at various separations of two rational surfaces of m/n = 3/1 double tearing mode is investigated quantitatively. Our study focuses on the explosive reconnection process where the exchange of island positions takes place and no secondary island forms. The negative dependence of explosive reconnection rate on resistivity in low resistivity and the systematic study of the effect of the separation on the resistivity dependence in high resistivity have been studied for the first time. The negative dependence is qualitatively different from the results in some relative studies where it usually exhibits a positive dependence on the resistivity or is independent of the resistivity. The negative dependence in two regions with a low resistivity, with a high resistivity and a large separation is caused by different reasons: one is the thickness of the current sheet, and the other is the separation.