Stainless　steel　was　ablated　by　a　10ps　Q-switched　Nd:VAN　pulsed　laser　(Austria)　in　air　under　different　operating　conditions　to　explore　high-efficiency　ultrafast　laser　micromachining.　The　relationship　between　the　ablation　characteristics　and　laser　parameters　(number　of　pulses,　fluence,　wavelength　and　repetition　rate)　was　analyzed　through　scanning　electron　microscopy　and　laser　scanning　confocal　microscopy.　The　saturation　pulses　are　approximately　2000-2500　in　our　experiments　at　varying　other　parameters　attribute　to　the　multi-pulse　damage　threshold　of　material.　A　critical　fluence　is　found　corresponding　to　the　deepest　hole　and　the　optimized　ablation　efficiency　which　is　related　to　the　formation　of　dense　plasma　at　the　surface　of　the　material.　The　short　wavelength　has　significant　advantages　for　the　holes　processing　with　high　aspect　ratios　because　of　the　lower　optical　absorption　coefficient　and　the　ablation　threshold.　Moreover,　the　maximum　ablation　depth　with　the　least　time　could　be　achieved　at　the　critical　repetition　rate　owing　to　heat　accumulation.　These　findings　are　expected　to　provide　guidance　to　improve　the　efficiency　of　ultrafast　laser　micromachining.