The　asynchronous　interconnection　between　Yunnan　Power　Grid　and　the　main　grid　of　China　Southern　Power　Grid　has　brought　a　series　of　frequency　stability　problems　to　the　main　grid　of　China　Southern　Power　Grid.　In　the　asynchronous　network　test　in　Yunnan　and　the　subsequent　DC　blocking　fault,　two　forms　of　frequency　oscillation　appear　in　the　power　grid.　One　type　of　oscillation　is　the　divergence　oscillation　occurring　near　the　rated　frequency　(f=50Hz),　and　Another　type　of　oscillation　occurs　in　the　vicinity　of　the　governor　dead　band　(f　=　0.05　Hz).　In　this　paper,　the　causes　of　these　two　forms　of　oscillation　are　analyzed.　When　comparing　the　effects　of　different　types　of　dead　band,　it　is　found　that　different　types　of　governor　dead　band　have　different　effects　on　the　same　input　signal.　Different　output　signals　are　analyzed　by　Fourier　analysis　method,　and　then　analyzed　by　damping　torque　method.　It　is　concluded　that　the　two　types　of　dead　band　have　different　amplitude　reduction　effects　on　the　mechanical　power　of　the　system,　which　affects　the　system　damping　size　and　stable　operation.　And　in　the　modified　four-machine　two-zone　system　model　for　time　domain　simulation,　the　results　also　prove　the　above　conclusions.　©　2019　IEEE.