The invention provides an adjusting device and method for the coating uniformity of a rectangular plane magnetron sputtering cathode. A baffle with a pore array is additionally arranged between a sputtering cathode and a workpiece plate. The pore array has different pore diameters at different positions. By changing the effective deposition area in a certain plasma etching rate, accurate control of the projected area of a plasma on the surface of workpiece is achieved, correction of the magnetron sputtering film thickness uniformity can be quickly and accurately realized, and the adjusting ofthe film thickness uniformity in the deposition area is realized.