The invention relates to an adjustable tray lifting device used for an automatic stock bin. The adjustable tray lifting device mainly comprises a workpiece clamping mechanism, a tray positioning mechanism and a tray lifting mechanism. The workpiece clamping mechanism adopts a three-rod-guided adjustable tray clamping technology. The tray positioning mechanism comprises needle bearing installation bases, needle bearings, an upper supporting base, a lower supporting base, a cylinder, an ejector head, a cylinder flange and a profiling block. The tray lifting mechanism comprises bottom plates, ejector polished shafts, linear bearings, a polished shaft upper fixing plate, ball screw nuts, a polished shaft lower fixing plate, ball screws, motors, bearing blocks, angular contact ball bearings, deep groove ball bearings and proximity switch supports. The bottom plates, the polished shaft upper fixing plate and the proximity switch supports vertically installed on the bottom plates are fixed through bolts, and fixation relative to the bottom plates is maintained. The adjustable tray lifting device has the advantages that the problem that use functions are affected due to large workpiece accumulative errors is effectively solved, production cost is reduced, high-efficiency energy conservation is achieved, the positioning position is precise, and the application range is wide.