This　paper　proposes　a　novel　in　situ　three-dimensional　(3D)　laser　machining　system　that　combines　3D　projection　algorithms　with　in　situ　measurement　and　3D　modeling.　This　system　forms　a　complete　＇scanning-modeling-projection-machining＇　integrated　processing　system　for　rapid　pattern　machining　on　the　free-form　surfaces.　In　situ　measurement　was　conducted　by　self-scanning　of　the　3D　galvanometer　scanner.　A　high-efficiency　Delaunay　triangulation　algorithm　was　employed　for　the　3D　reconstruction　to　generate　a　quality-controlled　3D　model.　The　Least-Squares　Conformal　Mapping　(LSCM)　and　As-Rigid-As-Possible　(ARAP)　algorithms　were　employed　for　model　parameterization.　Local　parameterization　and　bitmap　vectorization　methods　were　proposed　to　improve　the　accuracy　and　speed　of　parameterization　and　texture　mapping.　In　situ　machining　software　was　developed,　and　the　algorithms　were　verified　by　in　situ　machining　experiments.　The　LSCM　algorithm　achieves　fast　processing　speed　but　suffers　from　a　large　distortion　if　the　model　is　complex.　The　ARAP　algorithm　can　further　ensure　the　accuracy　of　the　parameterization　through　iterative　calculation.　The　developed　model　can　better　guarantee　the　model　quality　for　parameterization.　The　3D　projection　algorithm　can　transfer　the　two-dimensional　(2D)　pattern　on　a　3D　surface,　and　the　in　situ　method　eliminates　the　necessity　for　assembly　and　clamping　of　parts.　The　local　parameterization　and　bitmap　vectorization　methods　improve　both　the　accuracy　and　efficiency　of　3D　projections.　Therefore,　the　proposed　in　situ　machining　system　has　practical　application　value　for　the　rapid　processing　of　patterns　on　curved　surfaces.　©　2020,　Springer-Verlag　London　Ltd.,　part　of　Springer　Nature.