The invention belongs to the technical field of packaging equipment, and particularly discloses a sealing device for a packaging bag. The sealing device comprises a supporting unit, a feeding unit, anopening unit and a sealing unit. The supporting unit comprises a supporting table, and a communicating pipe and a suction nozzle are arranged on the supporting table. The feeding unit comprises a rotating shaft, a hopper and a storage pipe, a first rotating disc and a second rotating disc are arranged on the storage pipe, and the bottom of the storage pipe is connected with a discharging pipe. The rotating shaft sequentially penetrates the first rotating disc and the second rotating disc, a baffle and a rotating plate are fixed to the rotating shaft, and a discharging hole is formed in the rotating plate. A closed cam groove is formed in the surface of the rotating shaft. The opening unit comprises a piston barrel and a power mechanism, and a clamp rod is fixed to the piston barrel. A piston is in sliding connection in the piston barrel. An air pipe and a first one-way valve are arranged on the piston, and one end of the air pipe is connected with a suction cup. One side of a pipe ofthe piston barrel is connected with a pipeline, and a second one-way valve is arranged on the pipeline. According to the scheme, the device is simple in structure and low in cost, foods can be effectively packaged, and production efficiency can be improved.