The present invention provides a method for removing phosphorus and nitrogen contained in sewage or wastewater using iron ore wastewater. According to the method of the present invention, in which the phosphorus and nitrogen contained in sewage or wastewater are crystallized in the form of struvite using iron ore wastewater containing a large amount of Mg2+ produced in a process of upgrading low-grade iron ore and removed, it is possible to reduce the cost of Mg2+ and the cost of iron ore wastewater treatment, thereby earning economic profits. Moreover, it is possible to prevent water pollution by the removal of the phosphorus and nitrogen contained in sewage or wastewater. Furthermore, it is possible to use struvite crystals obtained as a by-product as a time-release compound fertilizer so as to reduce the amount of fertilizer used and the number of fertilizations, thereby reducing soil contamination.