In order to investigate the regulation mechanism of the initial setting time of the fly ash-based cementitious filling materials, the filling materials prepared with fly ash as the main body and sodium silicate and cement as auxiliary materials were designed based on the orthogonal experimental design method. Using polar analysis, analysis of variance (ANOVA) and mathematical regression fitting, we systematically analyzed the effects of three key factors, namely, the mass ratio of fly ash to cement (A), the dosage of sodium silicate (B), and the slurry mass concentration (C), on the initial solidification time of the filling materials. The research results show that the initial setting time range of fly ash-based filling materials is 19-69 minutes. The initial setting time shows A trend of first increasing and then decreasing with the increase of the mass ratio of fly ash to cement (A), shows a decreasing law with the increase of the dosage of sodium silicate (B), and shows a trend of rising - falling - rising again with the increase of the dosage of slurry mass concentration (C). The dominant chemical excitation effect of sodium silicate, as a strong alkaline activator, promotes the rapid dissolution of active components and their reaction with calcium ions generated during cement hydration to form a composite gel, causing the initial setting time to shorten exponentially with the increase of sodium silicate dosage.