Wire-arc additive manufacturing of magnesium alloys overcomes the main shortcomings of traditional casting and forging technology, which is a new technology in the field of magnesium alloy forming. However, the process of wire-arc additive manufacturing of magnesium alloys is affected by many factors, making it difficult to control the forming process. In addition, defects, such as hot cracking and pore defects, are prone to occur during the forming process. To solve this problem, a nonlinear relationship between the process parameters and the macroscopic morphology of the samples was established by combining experimental and machine learning methods. Furthermore, the influence of different process parameters on the forming quality was analysed, and the optimal ranges of process parameters were determined, i.e., 160 ℃ (substrate temperature), 12~14.5 m/min (wire feeding speed), 8~11 mm/s (travel speed), and 8~10 mm (weaving width). Finally, using AZ31 magnesium alloy wire as the experimental raw material, single-layer and multilayer magnesium alloy arc additive manufacturing experiments were conducted with the optimized process parameters. The experimental results reveal that the samples form well when the melt width is 13.95 mm, the melt height is 3.28 mm, the aspect ratio is 4.25, and the contact angle is 42°.