Abstract: Enclosed thin-walled circular structure was studied by CMT technology based WAAM. The overlaying mathematical model for single-pass multi-layer is firstly constructed on the basis of circular arc profile of single-pass single-layer; then an equal-volume melting metal for each layer was proposed and applied for actual manufacturing process and testified the feasibility. On account of the aforementioned model, the process parameters corresponding to the size of the thin-walled structure were also established and used for fabricating the parts. The enclosed thin-walled circular structure with fairly high appearance was obtained under the optimized process parameters. The scanned outline profile was also compared to the theoretical outline, and the results showed a good match between them.