In order to study the effects of nano-SiO2 and polypropylene fiber on the mechanical properties and water stability of coal gangue lime-fly ash mixture, the strength values of each specimen before and after modification were measured by unconfined compressive strength test and splitting test, and the quality difference, strength value and acoustic emission characteristics of the specimens after dry-wet cycle were analyzed. The results show that nano-SiO2 improves the compressive strength of the mixture, and the improvement effect is the best when the mass content is 2.5%. Adding nano-SiO2 and polypropylene fiber at the same time further improve the mechanical properties of the mixture. The mechanical properties of coal gangue lime-fly ash mixture are the best when 2.5% nano-SiO2 and 0.15% (volume fraction) polypropylene fiber were added. It is found that the water stability of coal gangue lime-fly ash mixture mixed with 2.5% nano-SiO2 and 0.10% (volume fraction) polypropylene fiber is the best.