In order to realize the comprehensive utilization of ferronickel slag and reduce the production cost of magnesium phosphate cement, ferronickel slag-based magnesium phosphate cement (MPC) was prepared through the reaction between ferronickel slag containing high MgO composition and ammonium dihydrogen phosphate. The influences of the mass ratio of ferronickel slag to ammonium dihydrogen phosphate m(FS/ADP), magnesium oxide content m(M/FS), water-to-binder ratio m(W/B), the dosage of boric acid m(B/FS) on the setting time and compressive strength of MPC were discussed under the condition of constant temperature water bath reaction at 50 ℃ for 8 h.The microstructures and phase compositions of hydration products of MPC were analyzed by using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), and the formation mechanism of MPC hydration products was speculated. The results show that when m(FS/ADP)=4:1, m(M/FS)=4%, m(W/B)=0.17, and m(B/FS)=0.3%, the working performance and mechanical properties of MPC were optimal. MPC was based on struvite gel and crystal as cementitious material, the particles of ferronickel slag were bonded and wrapped, and finally a high strength hardened body was formed. The hydration product was mainly struvite, and there was also schertelite.The result of material environmental safety performance evaluation shows that the total Cr leaching concentration in MPC was significantly lower than that of ferronickel slag, and far lower than the country standard(15mg/L), indicating that MPC has a certain sealing effect on heavy metals in ferronickel slag and improves its environmental safety performance.