Aiming at the problems of short pumping distance and easy plugging of gravel filling slurry in Datun Tin Mine, it was proposed to add copper slag tailings fine material to the gravel to improve the aggregate gradation, and the gravel-copper slag tailings mixture ratio test was carried out. It was concluded that when the proportion of gravel mass reached 60％, the packing density of mixed aggregate reached the maximum value. Further, through the strength test of backfill, rheological test, high concentration and high flow state test, the mix ratio of gravel-copper slag tailings paste was determined, which meets the strength requirement of filling body, no segregation of paste and self-leveling. Based on the actual filling situation of 32^# stope in Datun Tin Mine, the numerical simulation method was used to analyze the change law of pipeline resistance of gravel-copper slag tailings paste. The results show that the optimal mix ratio of gravel-copper slag tailings paste is gravel∶ copper slag tailings ＝ 6∶4, and the cement dosage are 270 kg/m³ (mass concentration 82％－83％), 240 kg/m³ (mass concentration 83％－84％), 210 kg/m³ (mass concentration 83％－84％), 180 kg/m³ (mass concentration 83％－85％), respectively. The resistance loss of gravel-copper slag tailings paste along the horizontal pipeline is 6 105.76－6 525.11 Pa/m, and the limit pumping horizontal distance is 2 298.81－2 456.70 m. The paste was used for industrial filling with a mix proportion of gravel∶ copper slag tailings ＝ 6∶4, a cement dosage of 240 kg/m³, and a mass concentration of 83％. Compared with the original filling process with multi-stage pumping, the paste with this mix ratio can meet the filling demand only under the condition of single pump, and the single pump conveying distance (2 052 m) is less than the limit pumping horizontal distance, allowing for surplus power at the outlet, which verifies the effectiveness of the optimal mix ratio.