The invention relates to a clamping device, in particular to a steel grating plate clamping device which comprises a hook plate, a clamping plate, an installation support, a clamping plate slider, a clamping cylinder, a first clamping rod, a second clamping rod, a third clamping rod, a fourth clamping rod, a sliding chute and a sliding guide block. The sliding guide block is arranged at the front end of the clamping plate and inserted into the sliding chute and can slide in the sliding chute. The front end of the first clamping rod is rotatably connected with the clamping plate slider, the back end of the first clamping rod is respectively connected with the second clamping rod and a cylinder body of the clamping cylinder through a pin shaft, the back end of the second clamping rod is rotatably connected with the installation support, the front end of the third clamping rod is rotatably connected with the clamping plate slider, and the back end of the third clamping rod is connected with the fourth clamping rod and a piston rod of the clamping cylinder through a pin shaft, and the back end of the fourth clamping rod is rotatably connected with the installation support. The steel grating plate clamping device is simple, compact and reasonable in structure; reliable in clamping and capable of avoiding error accumulation; convenient to maintain; and capable of avoiding oil leakage apt to happen due to oil cylinder clamping.