The　effects　of　spark　advance　angle　on　combustion　and　emission　characteristics　of　a　compressed　natural　gas　engine　have　been　investigated　experimentally　in　this　paper.　The　experimental　data　was　conducted　under　various　excessive　air　coefficient　conditions　using　an　electronic　ignition　system　developed　self-dependently.　The　results　show　that　the　peak　cylinder　pressure　and　peak　rate　of　pressure　rise　ascends　with　the　increase　of　spark　advance　angle　in　a　certain　extent,　and　their　corresponding　location　are　advanced.　The　CO　emission　keeps　almost　the　same　as　the　spark　advance　angle　varies　in　the　overall　mode　range.　The　HC　and　NOx　emissions　ascend　with　the　increase　of　spark　advance　angle　under　the　condition　that　excessive　air　coefficient　is　near　the　theoretical　value.　Under　the　lean-burn　condition,　the　HC　and　NOx　emissions　are　almost　the　same　while　the　spark　advance　angle　varies.