The invention belongs to the field of welding equipment and relates to a stainless steel tube butt welding machine for thin-walled stainless steel tubes. The stainless steel tube butt welding machine comprises a machine frame, wherein a main shaft is connected to the machine frame in a rotary mode, a lower clamping device is arranged on the top of the main shaft, an upper positioning cylinder is further mounted on the upper portion of the machine frame, and an upper clamping device is mounted on a downward-stretching piston rod of the upper positioning cylinder; a welder and a welding gun fixing base used for clamping a welding gun of the welder are further mounted on the machine frame. The butt welding machine further comprises a lower sleeve and an upper sleeve, wherein the lower sleeve and the upper sleeve are connected to the machine frame, a shielding gas inlet pipe communicated with an inner cavity of the upper sleeve is mounted on the lateral wall of the upper sleeve, and a shielding gas inlet pipe communicated with an inner cavity of the lower sleeve is mounted on the lateral wall of the lower sleeve. A through hole used for transmission of shielding gas is formed in the main shaft, and the top of the through hole penetrates out of the top of the main shaft and is communicated with an inner cavity of a pipe fitting to be welded. According to the stainless steel tube butt welding machine, product clamping processes are simplified, welding efficiency and quality are improved, oxidation inside and outside the pipe fitting is avoided after welding, and meanwhile, labor intensity of workers is greatly relieved, and product welding time is shortened.