Phosphorus removing method from waste water and preparation method of ferrous phosphate

The invention provides a phosphorus removing method from waste water. The method includes following steps: providing a solution containing phosphate anion; mixing a solution containing ferrous ions and the solution containing the phosphate ion and performing fluidized bed crystallization to obtian a ferrous phosphate precipitation, wherein a pH value of the fluidized bed crystallization is 5-6 and a molar ratio of the ferrous ion to the phosphate ion is 1.5-2.5 and a volume ratio of the solution containing ferrous ions to the solution containing the phosphate ion is 10-20; and removing the ferrous phosphate precipitation. The invention also provides a preparation method of ferrous phosphate. By means of the phosphorus removing method, damage of the waste water to environment can be reduced and meanwhile economic benefit is achieved. By means of the preparation method of the ferrous phosphate, the ferrous phosphate being low in water content, being high in purity and being high in crystallization rate can be prepared.