In　order　to　study　the　special　constriction　effect　and　physical　process　features　during　compulsively　constricted　WAAM　(CC-WAAM),　the　dynamic　behaviours　of　arc,　droplets,　and　molten　pool　were　visually　investigated.　Possible　interactions　inside　the　narrow　space　were　discussed　to　explain　the　mechanism　of　the　compulsive　constriction　on　ejected　plasma　and　droplets.　Based　on　the　captured　images,　the　strong　radiative　emission　indicates　that　the　ejected　plasma　was　at　high　temperature　at　least　6000　K.　As　the　current　increases　higher-temperature　plasma　jets　were　expected,　which　would　lead　to　a　larger　plasma　volume　in　the　absence　of　constriction.　The　relationship　between　current　and　droplet　diameters　was　preliminarily　established　to　enable　prediction　of　the　droplet　size.　An　important　feature　of　small-size　droplets　(as　low　as　0.89　mm)　offered　CC-WAAM　a　great　potential　to　improve　the　precision　of　the　additive　manufacturing　layers,　although　the　minimum　width　of　the　deposited　layer　is　much　larger　than　the　droplet　diameter　due　to　liquid　spreading　and　accumulation.　The　droplets　were　found　to　have　a　slight　impact　on　the　molten　pool　behaviours,　which　produces　stable　molten　pool　shapes.　Under　the　wide-range　parameters,　the　deposited　layers　showed　good　appearances,　which　indicates　the　good　adaptability　of　this　novel　technology.