Abstract: In order to meet the strength requirements of underground filling and plugging in grouting fire prevention materials, on the basis of slurry curing experiment of cement - coal ash grouting fire prevention materials, combined with X-ray diffraction analysis method, we study the influence of cement content on coal ash slurry initial setting time and compressive strength, and explore the formation mechanism of enhancing strength of coal ash slurry by cement. The results show that coal ash cement curing slurry is fast initial setting as the gray water ratio of 14︰10, the coal ash and cement addition ratio of 3︰1, adding 3 to 5 percent of the underground gelling curing agent, compressive strength of 2.91 MPa for 3 d, compressive strength of 7.50 MPa for 14 d, compressive strength of 7.95 MPa for 28 d, which fully meets the needs of underground filling and plugging. Hydration process of cement is synergistic interaction with coal ash hydration, which is the main reason for cement to enhance coal ash slurry by a dense interface structure.