The invention discloses a polymethyl methacrylate and stainless steel laser welding system. The polymethyl methacrylate and stainless steel laser welding system comprises a fiber laser, a laser head and an industrial computer, the laser head is electrically connected with the fiber laser and is capable of emitting a laser beam, and the industrial computer is electrically connected with the fiber laser and controls the fiber laser to conduct laser welding. The laser welding system further comprises a clamping device used for clamping a polymethyl methacrylate workpiece and a stainless steel workpiece. The clamping device comprises a lower pressing plate and upper pressing plates which are separated from each other and impact the two ends of each workpiece respectively, and the upper pressing plate can be used for adjusting the impacting degree for the workpieces through a screw rotation structure. The invention further puts forward a welding method using the polymethyl methacrylate and stainless steel laser welding system, so that the polymethyl methacrylate workpiece and the stainless steel workpiece can be tightly clamped so as to be effectively welded. Compared with the prior art, the polymethyl methacrylate and stainless steel laser welding system and the welding method have the advantages that the production yield is high, weld strength is high, welding deformation is small, precise welding is realized, and the like.