Abstract: In order to research the effect of magnetite tailing powder on the properties of cement mortar, the composite test of magnetite tailing powder, magnetite tailing powder and mineral admixtures (limestone powder, quartz powder and fly ash) were carried out.The test results show that the magnetite tailing powder has a negative effect on the fluidity of cement mortar, but an appropriate amount of magnetite tailing powder can enhance its bending strength; The strength of cement mortar decreases with the increase of the mixing ratio of magnetite tailing powder and fly ash.When the content of magnetite tailing powder is 10%, the contribution rate of mineral admixture to the unit strength is the highest, and the contribution rate of bending strength is higher than that of compressive strength.But when the content of magnetite tailing powder is more than 10%, the compressive strength has a negative effect.It is beneficial to the performance of cement mortar to increase the content of the composite gypsum with magnetite tailing powder.