The　surface　morphology　of　intra-layer　printing　process　plays　a　crucial　role　in　powder　bed　fusion.　It　not　only　determines　the　quality　of　the　top　surface　but　also　provides　insights　into　the　formation　evolution　during　the　building　process.　However,　the　formation　mechanisms　behind　diverse　surface　morphologies　and　their　correlation　with　build　quality　are　still　not　well　understood.　This　paper　presents　a　high-fidelity　model　of　electron　beam　powder　bed　fusion　to　depict　the　intra-layer　printing　process.　Four　typical　surface　morphologies,　namely　porous　surface,　even　surface,　swelling　surface,　and　labyrinth　like　surface,　were　reproduced　at　the　powder-scale　and　studied　in　terms　of　heat　and　mass　and　transfer.　Three　formation　mechanisms　involving　track　interaction　were　identified,　including　morphology　coalescence,　pre-heating　and　re-melting,　and　the　lateral　extension　of　melt　pool.　It　reveals　that　the　morphology　coalescence　effect　could　bias　the　current　track　towards　the　previous　track,　resulting　in　texture　along　the　hatch　direction.　The　pre-heating　effect,　caused　by　heat　accumulation,　improves　the　formation　quality　by　promoting　adequate　development　of　the　melt　pool.　Additionally,　the　re-melting　effect　could　further　enhance　the　formation　quality,　except　in　contour　tracks.　Particularly,　when　a　laterally　extended　melt　pool　spanning　several　adjacent　tracks　occurs,　it　could　produce　unique　surface　morphologies　due　to　the　lateral　convection　or　potential　central　break-up.　Finally,　the　top　surface　morphologies　of　intra-layer　printing　were　correlated　with　the　internal　build　quality　using　an　efficient　model　with　inter-layer　printing,　where　the　even　or　slightly　swelling　surfaces　were　found　to　correspond　to　a　good　build　quality.　This　could　enhance　the　understanding　of　build　mechanisms　and　contribute　to　the　improvement　of　metal　additive　manufacturing　processes.　©　2023　Elsevier　B.V.