This study evaluated the potential application of hydroxypropyl guar gum (HPG) and xanthan gum (XG) (HPG/XG weight ratio 1:1) to stabilize highly concentrated fly ash suspensions (FAS) (300 g/L) used for retarding spontaneous combustion of coal. The rheological behaviors of FAS were measured with different HPG/XG mixture concentrations including 1.2, 1.4, 1.6, 1.8, and 2 g/L, respectively. The effects of concentrations on the static stability of FAS were investigated to determine the optimal concentration. It was found that increasing HPG/XG concentration was beneficial to the viscoelasticity of FAS as evidenced by higher elastic modulus (G '), and FAS can be stabilized over 72 h when HPG/XG concentration increased to 1.6 g/L. Retarding spontaneous combustion experiments indicated that FAS significantly elevated the crossing point temperature of coal and reduced the carbon monoxide during low-temperature oxidation, efficiently retarding spontaneous combustion of coal.