Abstract: Fly ash grouting is a common method for mine fire prevention and control. Aiming at the problems of fly ash slurry which is prone to water-loss cracking, poor stability and low fire prevention efficiency, fly ash colloids were prepared by adding high molecular polymer xanthan gum (XG) and hydroxypropyl methyl cellulose (HPMC) to fly ash slurry, and the gel formation time, water-retaining property and thermal stability of fly ash colloids with different water-cement ratios were tested. The effect of colloid on the inhibition of coal spontaneous combustion was studied by programmed temperature. The results showed that when the water-cement ratio of fly ash slurry was 10∶1, the glue formation time was 9.52 min, and the water-retaining property and static stability were good. The fly ash colloid exhibited the shear dilution phenomenon of non-Newtonian fluid, and the energy storage modulus G′ was higher than the loss modulus G″. It was a pseudo-plastic fluid conforming to the power law model, and exhibited the properties of elastic solid. The weight loss process of fly ash colloidal heating can be divided into three stages (30-100 ℃, 218-380 ℃ and 380-800 ℃), and the total mass loss was about 6.17%. Fly ash colloid had the function of high moisture content, oxygen isolation and fissure sealing. The inhibition rate of coal sample after inhibition was 75.86%, and the corresponding temperature point of CO and C₂H₄ gas generation were 30 ℃ and 20 ℃ later than that of raw coal. The spontaneous combustion process of coal had been effectively inhibited.