The　paper　firstly　introduces　the　concept　of　spectrum　leakage　and　the　reason　for　spectrum　leakage.　Then　several　methods　proposed　to　reduce　the　spectrum　leakage　are　summarized.　When　the　sampling　frequency　is　invariable,　the　fluctuation　of　the　signal　frequency　can　make　the　measurement　of　the　harmonics　less　than　its　real　value,　at　the　same　time　the　non-existent　harmonics　can　be　analyzed.　Further,　a　new　adaptive　algorithm　of　equal　angle-interval　software　synchronous　sampling　is　proposed.　With　the　vector　theory,　the　adaptive　regulation　of　the　sampling　frequency　in　software　can　be　carried　out　through　the　harmonic　analysis.　Simulation　results　show　the　new　algorithm　not　only　greatly　reduces　the　spectrum　leakage　and　improves　the　accuracy　of　harmonic　analysis,　but　ensures　its　real　time　running　with　the　powerful　DSP,　thus　the　restriction　of　the　speed　of　DFT　is　resolved.　Moreover,　the　algorithm　has　great　application　potentials　in　the　fields　based　on　AC　measurement.