The invention provides a welding fixture for plastic piece laser welding. The welding fixture for plastic piece laser welding is characterized by comprising a bottom plate, a positioning plate locatedon the upper side of the bottom plate and used for placing a welding workpiece, a clamping plate located on the upper side of the positioning plate, and a drive unit for driving the positioning plateand the clamping plate to move along an Z-axis direction. According to the welding fixture for plastic piece laser welding provided by the invention, the clamping plate and the positioning plate canmove up and down, and a defocusing amount can be set through adjusting the heights of the clamping plate and the positioning plate, so that the flexibility in the welding process is greatly improved.