Ultrashort　laser　microwelding　is　an　advanced　technology　with　significant　potential　and　benefits　for　welding　dissimilar　materials,　including　ceramics　and　metals.　Details　of　the　microwelding　process　involving　ceramics　and　metals　with　ultrashort　lasers　remain　somewhat　unclear,　especially　regarding　phase　transformation　and　the　underlying　mechanism　of　joint　formation.　In　this　study,　we　utilized　the　ultrashort　laser　microwelding　technique　to　join　sapphire　and　Invar　alloy.　We　have　developed　a　predictive　numerical　model　to　calculate　the　interfacial　temperature　during　the　laser　irradiation　process.　The　relative　contributions　of　heat　diffusion,　heat　radiation,　and　heat　accumulation　in　the　welding　process　of　two　materials　were　investigated　under　single　and　multiple　pulses.　Upon　implementing　laser　pulse　energies　of　35,　40,　and　50　mu　J,　the　maximum　temperatures　of　sapphire　were　3027.8,　4179.89,　and　4533.30　K,　respectively.　The　maximum　temperature　of　the　Invar　alloy　exceeded　the　vaporization　temperature　(3223.15　K).　This　resulted　in　various　phase　transformations,　including　evaporation,　ionization,　and　melting,　that　occurred　on　both　substrates.　These　transformations　also　caused　the　intermixing　and　diffusion　of　materials.　It　then　resulted　in　the　formation　of　the　final　joint.　Based　on　the　findings,　we　aim　to　provide　a　more　comprehensive　understanding　and　practical　applications　of　the　ultrashort　laser　microwelding　technique.