In　this　paper,　by　investigating　the　laser-induced　plume　morphology　and　the　particle　signal　in　the　plume,　the　visual　signal　(average　area)　and　particle　signal　(number　of　particles,　average　velocity　and　total　signal　strength)　of　the　plume　change　with　the　input　energy　density　of　the　laser　was　studied.　The　weld　depth　is　positively　correlated　with　the　input　energy　density　of　the　fiber　laser.　Compared　to　the　average　area　of　the　plume,　the　plume　particle　signals　demonstrate　superior　consistency　under　varying　parameter　conditions:　during　changes　in　defocus　distance,　the　plume　average　area　is　negatively　correlated　with　the　laser　input　energy　density;　whereas,　in　other　variations,　a　positive　correlation　is　observed.　The　particle　signals,　under　different　parameter　conditions,　can　accurately　represent　the　positive　correlation　between　the　weld　depth　and　the　laser　input　energy　density.　Therefore,　the　particle　signal　in　plume　is　more　suitable　to　characterize　the　variation　trend　of　weld　depth　with　laser　input　energy　density.　In　the　three　kinds　of　particle　signals,　it　is　more　convenient　to　use　the　total　signal　amplitude　which　does　not　require　a　lot　of　calculation　to　characterize　the　change　of　weld　depth.