Abstract: In order to ensure the smooth transportation of high concentration filling slurry and the effect of accumulation in goaf, the rheological properties of high concentration filling materials were studied. This paper makes a preliminary study of the effect of cement and fly ash as cementitious materials and aeolian sand and loess as aggregates on the rheological properties of high concentration filling material under a series of samples with different binder-aggregate ratios. The relationship between the factors and the shear stress, apparent viscosity, yield stress, plastic viscosity, and thixotropy of the high concentration filling slurry was obtained. The results show that, high concentration filling materials with loess and aeolian sand as aggregate all have a certain thixotropy, and the larger the proportion of loess in aggregate, the greater the thixotropy. The shear rate and shear stress curve of the high concentration filling slurry are all subject to the Bingham model relationship either in the range of the shear rate increase interval data or the shear rate decrease interval data. The shear stress and the apparent viscosity increase with the increase of loess ratio at the same shear rate. We proposed to use the fine particle material (loess, cement and fly ash) and aggregate (aeolian sand) mass ratio to determine the rheological properties of the filling material. The greater the fine particle material and aggregate mass ratio, the smaller the yield stress, plastic viscosity and thixotropy, the better the slurry fluidity.