Abstract: Problems of big diameter pressure steel pipe welding in all position are discussed. Welding machine in all position is designed, including track,clipping equipment, weaving controlling circuit and tracing controlling circuit. In order to contact with gear and gear block the number of gear is not divided by three because the number of the gear block is three. For welding without groove, weaving time, weaving distance and stop time can be ehanged independently. Adopting to width of groove and auto groove tracing can be achieved by the sensor in tracing mode. The welding machine has been applied to weld pressure steel pipe in GUKOU water power station and 11-14# pressure steel pipes in three gorges hydro-electric power station suceessfully.