The invention discloses a leaf shearing device for bottom leaves of tobacco seedlings. The leaf shearing device comprises a rack, wherein a first cross beam, a second cross beam, a third cross beam and a fourth cross beam which are parallel with one another are mounted on the rack and can all slide in the corresponding length direction; the third cross beam and the fourth cross beam can move up and down relative to the first cross beam and the second cross beam; multiple groups of leaf shearing assemblies are uniformly mounted on the four cross beams, and multiple leaf shearing units are mounted on each leaf shearing assembly. All bottom leaves of the tobacco seedlings on one floating tray can be sheared off once for all, the bottom leaf shearing efficiency can reach 100 trays per hour, only one person is required to operate the leaf shearing device, the efficiency is greatly improved by comparison with conventional manual bottom leaf shearing, and the production cost is substantially reduced.