The invention discloses a welding device and method adopting coaxial in-situ compounded electric arc heat source and friction heat source, aims at realizing high-quality reliable connection under theconditions of a low rotational speed and a low mechanical load, and belongs to the technical field of welding. According to the welding device and method, a hollow high-melting-point metal friction stir welding tool is adopted, and the friction stir welding tool rotates and moves forwards along a welding joint during welding to implement a normal friction stir welding process; and meanwhile, an electric arc welding torch between electric arc tungsten electrodes accessed to a power supply and located in a hollow stir tool body heats the stir tool body, and electric arc energy is transferred toa welded area through a high-heat-conductivity cylindrical material at the center of a stir needle, and a stir tool body material. The welding device and method are capable of realizing reliable solid-phase connection for aluminum alloy and magnesium alloy members under the welding condition of no inclination angle, meeting the requirements of high rotational speed, high load and welding inclination angle of traditional friction stir welding on equipment, and improving the flexibility of the welding process and the quality stability of a joint.