Vaporizing　Foil　Actuator　Welding　(VFAW)　has　the　promising　potential　to　be　widely　used　to　join　steel　with　non-ferrous　metals,　such　as　titanium,　magnesium,　and　aluminum　alloys.　The　working　efficiency　of　aluminum　foils　used　as　the　medium　of　energy　transmission　from　electric　energy　to　dynamic　energy　during　VFAW　process　plays　an　important　role　in　the　welding　technique.　In　this　paper,　the　influence　of　the　working　efficiency　of　the　aluminum　foil　on　impact　velocity　between　the　flyer　and　target　was　explored　by　Photon　Doppler　Velocimetry　(PDV)　experiments.　The　experiments　were　carried　out　with　foils　of　three　different　thicknesses　under　varied　input　energies.　When　the　distance　between　the　fly　and　target　is　2.5　mm　with　the　impact　angle　of　5　degrees,　the　vaporization　energy　of　the　foil　is　the　key　factor　of　the　impact　velocity.　According　to　the　analysis　of　impact　velocities,　the　0.051　mm-thick　aluminum　foil　has　the　best　efficiency　with　the　input　energy　of　3　kJ,　0.076　mm-thick　aluminum　foil　works　most　efficiently　with　the　input　energy　of　3　to　6　kJ,　and　with　the　input　energy　of　6　to　12　kJ,　the　0.127　mm-thick　aluminum　foil　has　the　highest　working　efficiency.