The invention discloses a pearl size and roundness sorting device based on an equivalent algorithm. According to the pearl size and roundness sorting device disclosed by the invention, the pearl sizeis represented by an equivalent diameter, and the roundness is represented by the ratio of the perimeter to the equivalent perimeter. The pearl size and roundness sorting device disclosed by the invention sets up a pretreatment framework for performing segmentation denoising on an pearl image by adopting treatment methods such as median filtering, a Qtsu method and opening operation so as to forma calculation system which can perform perimeter solution and weighting based on an area pixel counting method, a boundary pixel counting method and an eight-chain code method. The pearl size and roundness sorting device adopts Matlab to write image processing software, meanwhile, a computer uses LabVIEW as a monitoring platform and invokes MATLAB to acquire the shape, size and roundness of pearlsand output the sorting results, and finally a PLC is used for controlling a mechanism to act, so that the mechanism can be used for sorting the size and roundness of the pearls according to set sorting standards. The pearl size and roundness sorting device disclosed by the invention can realize sorting of the size and shape of the pearls according to the set standards and send the pearls to different boxes by using an executing mechanism.