The invention relates to the technical field of powder preparation and processing and discloses a flow field construction method and a grading device used for particle grading. The method includes thesteps that uniform rotating gas flow and perturbation gas flow located below the rotating gas flow are correspondingly formed in a particle grading cavity, and therefore particles entering the particle grading cavity are firstly graded under the effects of the rotating gas flow, and then enter the rotating grading gas flow again under the effects of the perturbation gas flow to be graded. The flow field construction method for particle grading can perform more sufficient grading on the particles, and therefore the grading device applying the method has higher grading precision.