Experiments on YAG laser transmission welding of polymethylmethacrylate (PMMA) specimens are carried out to study laser welding technology, microstructure of welding zone and tensile property. The results show that transparent and black PMMA specimens can be well welded and there is no ablated mark at laser irradiated surface without optical absorbing material when laser power is above 200 W. In tensile experiments, the transparent PMMA specimens break at the edge of welding zone with the maximum load of 2110 N, and there is no crack at the welding zone. When laser power is below 200 W, the welding zone is fractured under the condition of single track welding, and the maximum load is 1170 N. Optical absorbing material can be used to improve the reliability of laser transmission welding of transparent and color PMMA specimens. The quality of laser transmission welding with black thermoplastic acrylic resin is better than that of other absorbing materials.