The　phase　lock　system　including　PCI　DAQ　card　and　PZT　was　studied,　which　is　based　on　the　principle　of　homodyne　coherent　optical　detection　and　LabVIEW　virtual　instrument　software.　The　system　overcomes　the　external　interference,　PZT　hysteresis　and　creep　effect.　Experimental　result　shows　that　the　fluctuation　of　the　locked　phase　is　no　more　than　3π/100　and　stability　time　is　no　less　than　3　minutes.　The　system　has　been　applied　to　the　coherent　light　communications.