Abstract: An all-position automatic minor-caliber pipe welding device used in a remote welding robot was designed for solving the problem of pipe maintenance in nuclear environment.The design analysis, working principle and automatic control parts of the device are described.The verification experiment about the device function was carried out by using the remote welding robot with the vision and force sensor.Results show that the device adapts the automatic assembling and disassembling requirement and has accurate position control.The circular motion error satisfies the demand of the all position welding.The actual welding results are good and prove that the device can be used in remote welding.