Abstract: In view of the quality control problem of surface forming in magnesium alloy arc additive manufacturing, process parameters of AZ91 magnesium alloy TIG arc additive manufacturing such as current, wire feeding speed and material increasing speed, and the width of cladding layer were modeled by Design-Expert software. The influence of various process parameters on the width of the additive layer was explored. The additive current was optimized by the mathematical model of the main process parameters and dimensions of the additive. Then the layer width of the straight wall component was controlled according to the current optimization value. The results showed that the greatest influence on the layer width was the additive current, followed by the additive speed, and the smallest influence was the wire feed speed. The layer width fluctuations of the single-pass multi-layer component prepared by the optimized process additively were small from top to bottom, and the layer width deviation value was reduced from 4.54 mm to 0.94 mm, which improved the quality of AZ91 magnesium alloy additive forming.Highlights: (1) Response surface method was used to analyze the influence of welding parameters on the TIG arc additive layer width of AZ91 magnesium alloy, and the relationship model between them was established.(2) Through optimizing the current parameters, the layer width control of AZ91 magnesium alloy single-pass multi-layer additive sample was realized, and the forming quality of the additive sample was improved.