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.　©　2021,　Editorial　Board　of　Transactions　of　the　China　Welding　Institution,　Magazine　Agency　Welding.　All　right　reserved.