Welding　penetration　control　is　crucial　for　weld　quality　control　in　GTAW　of　thin　plates.　Sensing　of　weld　depth　and　recognition　of　full　penetration　is　the　key　challenge　in　welding　penetration　control.　Conventional　direct　vision　sensing　of　full　penetration　at　the　back　side　of　weld　beam　can　effectively　extract　the　penetration　information,　but　often　cannot　be　used　due　to　the　limited　space　accessibility.　Therefore,　in　this　paper,　welding　penetration　control　based　on　arc　voltage　sensing　was　studied.　By　extracting　the　penetration　features　during　arc　voltage　sensing　as　a　feedback,　the　welding　current　waveform　could　be　modulated　to　adjust　the　welding　depth　in　real　time　and　thus　to　ensure　uniform　weld　full　penetration　without　burning　through.　The　bead-on-plate　welding　experiments　were　conducted　using　4　mm　thick　hot　rolled　steel　plates　and　3　mm　thick　cold　rolled　steel　plates.　Control　principle　was　verified　by　enforcing　the　bead-on-plate　welding　experiments　under　different　welding　currents.　Sound　welding　seams　was　acquired　in　variational　cooling　condition　and　variational　clearance　bead-on-plate　welding　experiments.　Test　results　show　peak　voltage　time　can　be　controlled　according　to　the　intelligence　feedback　of　arc　voltage.　©　2018,　Editorial　Board　of　Transactions　of　the　China　Welding　Institution,　Magazine　Agency　Welding.　All　right　reserved.