The invention discloses a clamping device of a laser cutting machine. The clamping device comprises a fixed seat, and two fixed blocks are symmetrically and fixedly mounted at the top of the fixed seat. First through holes are formed in the close sides of the two fixed blocks, and fixed rods are fixedly mounted in the first through holes. The far ends of the two fixed rods extend out of the two first through holes correspondingly, and first grooves are formed in the close ends of the two fixed rods. Movable rods are mounted in the first grooves in a sliding manner, and one ends of the movablerods extend out of the first through holes. Screw holes are formed in the far ends of the two movable rods, and lead screws are arranged in the screw holes. The lead screws are in threaded connectionwith the screw holes, and one ends of the lead screws extend out of the screw holes. According to the clamping device, clamping blocks can be conveniently and fast moved to stably clamp a workpiece, use by an operator is convenient, the clamping blocks can be fast replaced to clamp the workpiece according to the shape of the workpiece, and high practicality is achieved.