Droplet　state　and　transition　process　directly　determine　the　forming　quality　of　deposited　layer　in　wire　and　arc　additive　manufacturing(WAAM).　In　this　study,　an　in-situ　measurement　system　of　the　droplet　state　(temperature,　velocity　and　mass)　at　plasma　arc　was　established.　An　innovative　staged　heating　method　was　proposed　to　reduce　the　measuring　error　of　droplet　temperature　caused　by　the　plasma　arc.　Meanwhile,　a　trajectory　fitting　method　was　studied　to　predict　the　droplet　velocity,　because　droplet　morphology　was　difficult　to　keep　consistent　during　the　transferring　process.　Then,　the　effect　of　current　and　plasma　gas　rate　on　the　droplet　state　measurement　were　studied.　This　study　will　provide　an　effective　measurement　method　for　the　droplet　state　in　the　high　temperature　plasma　arc　environment.