Electronic　ballast　is　the　important　part　of　high　pressure　sodium　lamp.Start-up　mode　of　high　pressure　sodium　lamp　is　the　difficulty　in　this　areas.Start-up　voltage　must　higher　than　working　voltage　when　the　lamp　start-up.Power　supply　voltage　is　not　high　to　start-up　the　high　pressure　sodium　lamp.So　we　need　voltage　transformer,　pulse　generator,　resonance　circuit　and　so　on　to　generate　the　start-up　voltage.　We　analyse　the　theory　of　electronic　ballasts　of　high-pressure　sodium　lamp　and　make　experiments　in　this　paper.　We　have　developed　the　sample　of　high　pressure　sodium　lamp　based　on　this　theory,and　got　the　obvious　effect　in　energy-saving.