In　order　to　improve　the　surface　quality　of　KDP　crystals,　the　factors　of　process　parameters　on　surface　quality　of　KDP　crystal　was　researched,　the　KDP　crystal　was　machined　by　quadratic　regression　rotation　optimization　method　and　single　point　diamond　turning　technology.　On-line　monitoring　the　surface　roughness　and　waviness　of　KDP　crystal,　using　multi-factor　interaction　to　get　analysis　rules.　Finally,　partial　least　squares　method　and　lingo　software　were　used　to　obtain　optimal　processing　program,　the　tool　radius　of　9mm,　speed　of　800　r　/　min,　feed　rate　of　9.184　mu　m　/　r,　turning　back　of　21　mu　m.　With　these　process　parameters　to　machine　KDP　crystal,　surface　waviness　can　be　achieved0.020　mu　m,　and　surface　roughnesscan　be　achieved　0.017　mu　m,　has　important　guiding　significancefor　machining　large-size　and　high　quality　KDP　crystals.