The invention discloses a method for preparing a porous-structure material through mixed roasting. The method is characterized in that pyrite and limonite are used as raw materials and are mixed or granulated according to a mass ratio of 3:1-1:1; roasting is conducted at the temperature of 550 DEG C-800 DEG C under the anaerobic condition; and the material with the porous-structure characteristic is obtained, wherein the phase of the material is mainly composed of nanometer-submicron crystal particle size pyrrhotite. The material has nanometer and micron clearances and high specific surface area and is used as an active filter material to recover heavy metal from waste water and treating the waste water and eutrophic water to achieve simultaneous removal of nitrogen and phosphorus.