The invention discloses a method for welding a noise-reduction exhaust pipe. The method comprises the following steps: (1) enabling the pipe orifice of a gas inlet pipe to extend to a mounting hole, used for mounting the gas inlet pipe, of a buffer tube, and performing electric welding to enable the gas inlet pipe and the buffer tube to be fixedly connected; (2) enabling a truncated-cone-shaped section of an auxiliary gas outlet part to extend into the buffer tube from a sleeve hole of the buffer tube, and after the whole truncated-cone-shaped section extends into the buffer tube, welding the auxiliary gas outlet part onto the buffer tube through electric welding. The method provided by the invention is simple to operate, good in welding quality and easy to implement and popularize.