The invention relates to a combined and staged separation method for weathered phosphoric ore, in particular to a method for stage floatation of the phosphoric ore according to volume density variation. The method comprises the following technical steps of: (1) crushing the weathered phosphoric ore to ensure that more than 80 percent of grains have the grain size of less than 0.074 mm, blending the pulp until the mass concentration is 27 to 40 percent, and adding a stage synergist; (2) introducing an agitation type floatation machine for the stage floatation; and (3) taking grains adhered to bubbles and floated as light components, putting the grains serving as floatation feeding into a light component floatation system, and taking grains discharged with a underflow as heavy components and putting the grains serving as floatation feeding into a heavy component floatation system to respectively obtain light component phosphate concentrate and heavy component phosphate concentrate. The separation method has the advantages of simple process, capability of separating the light components, high stage efficiency, easy operation and easy realization of industrialized production.