The invention provides a fully-automatic tray loader for cylindrical lithium ion batteries. The fully-automatic tray loader comprises a rack, a loading trolley, an empty tray lifting mechanism, an empty ray transfer mechanism, a tray positioning mechanism, a battery cell rotary-grabbing mechanism, a battery cell reshaping mechanism, an automatic grabbing and placing mechanism, a full-load tray transfer mechanism, a full-load tray lifting mechanism and an unloading trolley, wherein the empty tray transfer mechanism and the full-load tray transfer mechanism share a double-tray transverse moving part for transferring an empty battery cell tray at the lower end of the empty tray transfer mechanism to the tray positioning mechanism and transferring a battery cell tray which supports and is filled up with circular battery cells to the lower end of the full-load tray transfer mechanism. Through the mechanisms, the empty battery cell trays are transmitted to the tray positioning mechanism for being positioned, are automatically loaded with the reshaping battery cells, are automatically transmitted, superposed and stacked onto the unloading trolley, and are in fully-automatic butt joint with an automatic winding machine for manufacturing circular batteries or battery cells, so that multiple functions are integrated, manual tray loading is completely replaced, production efficiency is improved, and labor power is saved.