The invention discloses an online cleaning device for a lower pressing roll of a glass pressing machine. The online cleaning device is arranged on a pressing frame below the lower pressing roll and structurally comprising a spraying pipe with more than two nozzle groups, each nozzle group comprises a plurality of nozzles, the nozzles of each two adjacent nozzle groups are in staggered array in the direction of the center line of the lower pressing roll, and liquid level of liquid sprayed by each nozzle group is above the vertical plane. The spraying pipe is provided with a liquid inlet, and cleaning liquid with a certain pressure is delivered into the spraying pipe through the liquid inlet and sprayed by the more than two nozzle groups to form more than two rows of liquid levels to clean an operation surface of the lower pressing roll. Compared with the prior art, the online cleaning device has the advantages that one-time integral cleaning can be realized, cleaning effects are enhanced, cleaning operation time is shortened, cleaning efficiency and operational stability are improved, and high applicability is achieved; in addition, the online cleaning device is simple in structure, convenient to mount and demount and convenient for large-scale industrial popularization and promotion.