The invention discloses a rotor screen preparing device. The rotor screen preparing device comprises a positioning core mold, a welding locking mechanism, a turning mechanism, a pulling-out demouldingmechanism, and a clamping device, wherein the positioning core mold is used for being sleeved with a rotor screen assembly, and the rotor screen assembly is composed of a rotary disc flange, left andright scraper plates, a screen body and a screen upper flange; the welding locking mechanism is used for locking the positioning core mold and the rotor screen assembly before welding; the turning mechanism is used for turning the rotor screen assembly after welding; the pulling-out demoulding mechanism is used for separating and demoulding the rotor screen assembly and the positioning core moldafter turning; and the clamping device is used for fixing the rotor screen assembly during separating and demoulding, the positioning core mold is of a hollow structure, a large thread hole and a small thread hole are formed in the two end surfaces of the positioning core mold correspondingly, and a step positioning hole matched with a spindle chuck of the turning processing mechanism is formed inthe large thread hole. By means of the rotor screen preparing device, the machining accuracy can be improved, the number of the holes and is increased, the hole diameter is reduced, the mesh number of a rotor screen is increased, and the crushed whole particles are finer accordingly.