The invention discloses a tool for assembling front and rear charging barrels of a powder tank truck. The tool comprises a bottom frame whose long edge is along a left-right horizontal direction, theright side of the bottom frame is provided with a linear guide rail. The linear guide rail is slidably provided with a mobile frame. The left end of the bottom frame and the right end of the mobile frame are respectively vertically provided with end loop arms. The upper part of each end loop arm can be opened. The middle position of the bottom frame, close to the left end, and the left end of themobile frame are respectively vertically provided with middle loop arms. The upper part of each middle loop arm can be opened. The outer walls on the left side and right side of the bottom frame are vertically provided with a left side support and a right side support. The two side supports are slidably provided with sliding blocks. The sliding blocks are provided with infrared opposite pipes in an embedded manner. A slanting lower position and a slanting upper position of the left side end loop arm and the right side end loop arm are respectively provided with infrared opposite pipes in an embedded manner. The tool can realize semi-automatic assembly. Relative offset directions and offset quantity can be obtained when assembling. A crane is not needed. The tool and the method can improveproduct quality and consistence, and improve production efficiency.