Abstract: In view of the problem that the water gushing problem of deep coal mine roadway seriously affects the safety of coal mine construction, and the common cement grout is difficult to seal up the tiny rock cracks, the micron-grade fly ash is used to replace part of superfine cement, polycarboxylate superplasticizer and nano-CaCO₃ admixture are used to improve the performance of composite slurry. The results show that the slurry properties vary with the water-cement ratio, and are negatively correlated with the initial viscosity, hardened rate and strength, while positively correlated with fluidity. The appropriate addition of nano-CaCO₃ made the strength slightly improved, but the viscosity, fluidity and hardened rate did not change significantly. The addition of micron-grade fly ash reduces the viscosity, hardened rate and strength, and appropriately improves the fluidity. The polycarboxylate superplasticizer was positively correlated with fluidity and negatively correlated with stone rate, but had little effect on viscosity and strength. The change of slurry viscosity with time can be divided into two stages: stable period and rising period. The viscosity change rate of stable period does not exceed 15.5%.