Abstract: The nitrogen content in the weld for FACW-S (flux cored arc welding-self-shielded)is about 0.025%-0.035%, which is higher than other welding materials.The effects of flux ingredients(for example:fluoride, carbonate and nitrogen fixation substance Al)on the nitrogen gas pore were studied.The welding parameters also have an important influence on the nitrogen gas pore. Considering the gas pore in the weld, the welding parameters should be 220 -280 A welding current, 18-24 V welding voltage, 20 - 30 mm wire extension and direct current stright polarity.Hydrogen gas pore and CO CO₂ gas pore are not easy to form in FCAW -S weld.