Abstract: Oxygen content 0, nitrogen content N and residual hydrogen content Hr in weld metal were meassured using SQM-PWSE heating gas chromatography welded by φ1.6 mm H08Mn2Si welding wire with mixed gas arc welding. With the increasing of CO₂ content in protective atmosphere, O, N and Hr increase. With the increasing of welding current, O, N and Hr decrease. The mathematical relationship between O, N, Hr, and CO₂ content in protective atmosphere and welding current is established based on the tropical analysis.The value of O,N and Hr calculated by this model is well consistent with experimental results. This model can be used to qnantitatively calculate O, N and Hr on the given condition.