Abstract: In order to study the optimum mixture ratio and mechanical properties of fly ash solidification filling material, orthogonal method was used to test the fluidity, initial and final setting time and compressive strength of the mixture material including water, sodium silicate and slaked lime. We obtained the optimal ratio of fly ash solidification filling material. Experiments show that deformation and failure of fly ash filling material are divided into four stages: compaction stage, yield stage, plastic deformation and destruction stage, which presents a linear elastic deformation stage and deformation characteristics of reinforced plastic stage, basically without softening stage.