Abstract: One of the technical problems of paste backfill is how to prepare a stable and suitable underflow in the pro‐cess of tailings thickening，so as to meet the needs of subsequent process links and provide technical support for safe and ef‐ficient production in mines.However，in actual engineering，the underflow concentration of the tailings thickening is often un‐stable. Based on the latest research progress in the field of tailings thickening，it is found that the underflow concentration is affected by the macroscopic factors of the thickening process，and the root cause depends on the microscopic view of the floc structure during the thick dehydration process. Therefore，by reviewing domestic and foreign research progress of tailings thickening in tailings flocculation，tailings floc structure change，floc water content change，bed pore channel development and evolution，and compaction zone dewatering，systematic analysis of the mechanism of the external conditions on the change of the floc structure in the dense，the cause of the change of the floc water content by the structure of the floc，the influence of the floc water and the pore channels in the compaction zone on the underflow concentration，it is concluded that the flocculation conditions determine the initial form of the floc structure，the fluid shear force in the settlement zone，the pressure of the tailings bed in the compaction zone and the shearing effect of the rake change the structure of floc，the water content of the floc will change with the change of floc structure，it changes and is discharged through the pore channels of the bed to increase the underflow concentration of the thickener. Furthermore，based on the research progress at home and abroad，the microscopic effect of the change of floc structure on the thick dewatering of tailings is deeply discussed，and the current problems and future development trends of tailings thickening of dewatering are put forward.

Key words: paste backfill, thickening of tailings, floc structure, floc water, drainage channel