Abstract: Rheological properties of filling slurries cemented phosphate tailings with cement and CFBC ash are researched by fluidity instrument and rotary viscosimeter.The results show that rheological properties of filling slurries with phosphate tailings-cement-CFBC ash conformed to Bingham plastic fluid characteristics, and thixotropy of the filling slurries is very small.Increasing the content of CFBC ash, the fluidity of slurry reduces and plastic viscosity increases.When the binder-sand ratio is reduced to 1∶8 or the mass concentration is as high as 76%, the influence of the amount of CFBC ash on the fluidity and apparent viscosity is significantly reduced.When the mass concentration of slurry is 74%, the yield stress is positively correlated with the content of CFBC ash and the binder-sand ratio.The content of CFBC ash has no significant effect on the yield stress for slurry with the mass concentration of 76%.When the binder-sand ratio is 1∶5-1∶6, to ensure the smooth pumping of slurry with mass concentration of 76%, the content of CFBC ash should be controlled within 40%.