Taking the Henry gangue slag heap management project as an example, and aiming to optimise the proportioning of the grouting fire extinguishing slurry to improve the effect of spontaneous combustion management of coal gangue. P. O32.5 ordinary silicate cement and F class Ⅱ fly ash were selected as the main materials for the experiment, and the effect of slurry proportioning on its performance was investigated by orthogonal test method. Taking the water-solid ratio (A) and cement-solid ratio (B) as variables(3 levels each), L₉(3²) orthogonal test table was constructed to test the slurry fluidity, water precipitation rate, stone formation rate, setting time and other indexes. The test results show that the water-solid ratio and the cement-solid ratio have a significant effect on the performance of the slurry. The slurry fluidity is positively correlated with the water-solid ratio and negatively correlated with the cement-solid ratio. The water precipitation rate is negatively correlated with the cementation rate, and the water-solid ratio has a greater influence on it. The setting time is positively correlated with the water-solid ratio and negatively correlated with the cement-solid ratio. According to the experimental results, the best slurry ratio was determined, and combined with the gangue characteristics of the mining area, the ground injection hole material proportioning scheme was proposed for different boosting stages. Through the local fire extinguishing and isolation zone test verification, the management effect is good, the leakage of boreholes is slow, and the temperature of slag heap is gradually reduced, which provides an effective technical reference for the management of coal gangue spontaneous combustion.