Abstract: The effects of different caustic calcined magnesias on the potash tailings cementation were analyzed according to the nature of light burned magnesium oxide (grade 65,70,75,85),and the effects of operating conditions on the gelation time,fluidity,rheological properties and physical parameters during the process of cementing tailings were also investigated.The results showed that the caustic calcined magnesia of grade 65 was the most suitable gelling agent in the backfill of the potassium tailings.Meanwhile,the gelling effect became better with the increase of gelling agent dosage and the reduction of curing time.Temperature was found to have direct effect on the reaction rate and viscosity,and low temperature did not favor the gelation reaction and paste cementing performance.By studying the effect of impurity (CaO and NaCl) on gelling process,CaO was found to be able to accelerate the cementation reaction and enhance the water-holding capacity performance of cemented paste.