The　femtosecond　laser,　which　induces　periodic　microstructures　on　the　surfaces　of　metallic　materials,　is　extensively　applied　in　photovoltaic　power　generation,　self-cleaning,　and　biomedical　fields.　In　this　paper,　we　fabricate　periodic　microstructures　on　the　surface　of　Ti　by　utilizing　a　green　femtosecond　laser　with　a　power　of　75　W,　a　pulse　width　of　800　fs,　and　a　wavelength　of　515　nm.　First,　the　ablation　threshold　of　Ti　under　the　line-scan　condition　is　discussed　herein.　The　Ti　surface　microstructures　are　induced　based　on　a　90°　cross-surface　scan　processing.　We　derive　the　formula　for　the　calculation　of　the　effective-pulse　number　per　unit　point　in　the　surface　scanning　and　summarize　the　microstructural　evolution.　The　results　obtained　demonstrate　the　following:　1)　the　ablation　threshold　of　Ti　by　utilizing　the　green　femtosecond　laser　is　significantly　lower　than　that　of　the　previously　reported　long-wavelength　infrared　laser;　2)　the　surface　microstructure　of　Ti　can　be　attributed　to　the　effective-pulse　number　per　unit　point　and　the　laser　fluence　in　the　surface　scanning.　Due　to　the　increase　in　the　effective-pulse　number,　the　microstructure　changes　from　nonuniform　distribution　of　hump　to　uniform　columnar　array　structure　when　the　laser　fluence　is　low,　or　to　interconnected　hilly　structure　when　the　laser　fluence　is　high.　The　similar　structure　can　be　obtained　either　by　applying　a　high　laser　fluence　and　small　effective-pulse　number,　or　a　low　laser　fluence　and　large　effective-pulse　number.　The　former　can　significantly　increase　processing　efficiency.　©　2019,　Chinese　Lasers　Press.　All　right　reserved.