Violent　eruption　of　spatters　is　one　of　the　major　problems　restricting　fiber　laser　keyhole　welding　technology　development.　In　this　study,　the　fiber　laser　power　density　variation　was　attained　by　altering　the　laser　power　and　laser　spot　diameter　for　analyzing　its　impact　on　the　eruption　of　spatters.　The　severity　of　spatters＇　eruption　can　be　indicated　by　the　number　of　spatters　and　the　mass　loss　of　the　weld　seam.　The　correlation　between　the　number　of　spatters　and　laser　power　density　can　be　positive　(if　the　latter　is　adjusted　by　changing　the　laser　power)　or　negative　(if　the　laser　power　density　is　varied　by　changing　the　laser　spot　diameter).　When　the　latter　diameter　is　changed,　it　has　a　strong　impact　on　the　vapor　induced　by　the　laser　on　the　front　keyhole　wall　(FKW),　the　FKW　inclination　angle,　and　the　molten　pool　surface　tension.　The　number　of　spatters　also　positively　correlates　with　the　laserinduced　vapor　on　the　FKW　or　the　molten　pool　width　and　negatively　correlates　with　the　FKW　inclination　angle.　Reducing　the　laser　spot　diameter　can　increase　the　laser　power　density,　enhancing　the　welding　process　stability　and　suppressing　the　eruption　of　spatters　to　a　certain　extent.