As the waste of power plant,widely distributed ultra-fine fly ash is of small modulus of fineness, hence improves the fluidity and groutability of cement slurry by mixing with cement. In this paper, orthogonal tests were carried out with water cement ratio, ultra-fine fly ash content and sodium silicate content as main factors. The physical properties such as gelation time, viscosity and stone rate of the slurry were determined. On the basis of range analysis, variance analysis and regression analysis results, a new type of fly ash cement slurry with controllable gelling time was developed, and the formula of predicting gelling time was regressed. Finally, the groutability of the slurry is examined through model test. The research findings demonstrate that ultra-fine fly ash cement slurry with water cement ratio as 0.8, ultra-fine fly ash dosage 70%, and sodium silicate content 15% is of fast gellation and good viscosity, and better grouting performance compared with ordinary cement slurry.