Abstract: In order to solve the problem of vegetation restoration caused by the lack of nutrients and poor water and fertilizer retention capacity of iron tailings，and to realize the high value utilization of agri⁃ cultural waste，corncob is used as raw material to prepare functional biochar by synergistic modification of potassium dihydrogen phosphate and diammonium phosphate.The effects of functional biochar on the physi⁃ cal and chemical properties of iron tailings and the growth of ryegrass are systematically investigated by SEM，FTIR characterization and pot experiment.The results show that phosphate synergistic modification makes biochar form macro-mesoporous / microporous hierarchical structure，increases surface roughness and active sites，and successfully anchors phosphorus-containing functional groups（PO4 3- ），which signifi⁃ cantly optimizes the microstructure and chemical properties.After adding modified biochar，the water reten⁃ tion，fertilizer retention and ventilation conditions of iron tailings are improved.The early germination rate， plant height and biomass of ryegrass are significantly higher than those of the control group.The germina⁃ tion rate of 6 d is more than 80%（about 50% of the control group）. The maximum wet weight and dry weight of 24 d ryegrass are 0.449 g and 0.029 g，respectively，and the plant height is concentrated in the high value range of 5~16 cm.The effect of biochar remediation is closely related to the dosage，and 1%~3% is the best dosage range.Excessive dosage（5%）will inhibit the growth of ryegrass.The preparation and ap⁃ plication technology of corncob-based phosphate co-modified biochar proposed in this paper provides a new path of economic，environmental protection and sustainability for the ecological restoration of iron tail⁃ ings，which has both ecological benefits and resource recycling value.

Key words: phosphate synergistic modification, corncob biochar, iron tailings, ecological restoration, ryegrass