The invention provides a double-light-path ultrafast laser welding device based on light beam shaping. The double-light-path ultrafast laser welding device comprises a femtosecond laser, a half-wave plate, a polarization splitting prism, an electric control shutter, a laser beam expander, a first holophote, a dichroscope, a galvanometer system, a field lens, a to-be-welded sample and an XYZ movable welding platform. Gaussian beams emitted by the femtosecond laser sequentially pass through the half-wave plate, the polarization splitting prism, the electric control shutter, the laser beam expander, the first holophote, the dichroscope, the galvanometer system and the field lens and then are gathered on a to-be-welded sample, and the to-be-welded sample is fixed on the XYZ movable welding platform to form a Gaussian light beam welding light path. A Bessel light beam conversion system is arranged between the first holophote and the dichroscope to form a Bessel light beam laser welding light path. The invention further provides a machining method using the device. According to the welding device, double-light-path welding of different laser beams is achieved, the welding device is suitable for non-optical contact welding and optical contact welding, the welding quality can be effectively improved, and the production cost can be effectively reduced.