The invention discloses a tool for laser welding of a printed circuit heat exchanger (PCHE). The tool for laser welding of the printed circuit heat exchanger comprises a base, a top cover, positioning pins, fastening studs and guide rods, wherein the base and the top cover are connected through the positioning pins, the fastening studs are arranged at the four corners of the base and the four corners of the top cover, and the guide rods are located on the two sides of the middle. The positioning pins vertically penetrate through multiple layers of the PCHE metal heat exchange plates which are located between the base and the top cover. The top cover and the base are connected in a fastened through the studs and tightly clamp the metal heat exchange plates located between the top cover and the base. The positioning pins are ejected out of the metal heat exchange plates through pin retreating screws, so that the shearing stress between the metal heat exchange plates is zero when the heat exchange plates of the tool are taken out, and thus the metal heat exchange plates are prevented from falling into pieces when the PCHE is taken out. According to the tool for laser welding of the PCHE, the technical requirements for strictly aligning the metal heat exchange plates of the PCHE, tightly clamping the metal heat exchange plates of the PCHE and conveniently taking a welded heat exchanger core out of the tool are met.