Abstract: The weld formation and its influence factors of arc welding with shelf-shielded flux-cored wire in low atmospheric pressure areas were studied. The research results show that at the same welding parameters, the lower atmospheric pressure is,the more shallow the weld penetration depth is, the wider the weld width is,and the lower the weld reinforcement is. Due to weakened cooling effect to the arc by low atmospheric pressure, arc diameter increases compared with the normal pressure, arc stability and stiffness decrease. The change of the arc behavior influences the weld formation. The symmetry of weld formation becomes poor. The increase of welding torch height has negative influence on weld formation and arc stability as well. The increase of wire feeding rate and decrease of arc voltage in a certain range can be good for improving the weld quality. The research results provide scientific basis for formulating welding process specifications and parameters optimization of arc welding with self-shielded flux-cored wire in low atmospheric pressure areas.