Abstract: In order to reduce the cost of full tailings cement filling，research and practice on the in⁃ fluence of the reduction of the ratio of cement to sand on the compressive strength of the backfill were car⁃ ried out by optimizing cementing agent in Longqiao Mining. The results showed that under the condition of ensuring the filling strength，the optimization of the cementing agent could reduce the ratio of cement to sand from 1∶6 to 1∶8 and the amount of cement by 36.2 kg per cubic meter of filling. The cost of filling ma⁃ terials on average per year saved by 10.86 million yuan. The following studies also showed that the ratio of cement to sand can be further reduced to 1∶10，the amount of cement can be reduced by 23.04 kg per cu⁃ bic meter of filling，and the production cost also will be further reduced.

Key words: tailings filling, cement filling, ratio of cement to sand, cementing agent