Research on recycling waste printed circuit boards is at the forefront of preventing environmental pollution and finding ways to recycle resources. A wet process for reclaiming metals from printed circuit boards applying a tapered diameter separation bed is described, and the separation mechanism of the device is proposed. The motion of a particle in the tapered diameter fluid flow field and particle separation within this field were studied. As the material passes through the fluid field, along with the water, differences in particle density, granularity, and shape cause particles to follow at different trajectories. A tapered diameter separation bed was used to process 1–0.074 mm-sized crushed material from discarded printed circuit boards. The separation efficiency of 91.77 % and the recovery rate of 95.79 % for recovered metal were achieved with a discharge water flow rate of 4.5m3/h, a material feed rate of 300 g/min, and an obliquity of 30°. For −0.074 mm printed circuit boards, the metal recovery is 93.42 % and the separation efficiency is 77.63 % when the water discharge is 2 m3/h, the obliquity is 35º, and the material feed rate is 450 g/min. The superfine products in a size range of −0.074 mm can be recovered effectively under suitable operating condition using the tapered diameter separation bed. It indicates that the lower separation limit of the tapered diameter separation bed can be close to zero. The technique will prevent environmental pollution from waste printed circuit boards and allow efficient recovery.