An　improved　DFT　algorithm　based　on　reference　phase　is　presented　for　purpose　of　accurate　detection　of　positive　fundamental　active　and　reactive　currents　under　complicated　conditions.　Using　this　algorithm　mentioned,　the　fundamental　voltage　and　current　and　the　corresponding　orthogonal　component　can　be　reconstructed　under　the　αβ　reference　frame.　Then　the　fundamental　positive　sequence　active　and　reactive　current　were　extracted　by　the　instantaneous　symmetrical　component　method　and　the　instantaneous　reactive　power　theory.　Considering　frequency　fluctuation　of　power　grid,　the　frequency　variation　was　tracked　online　with　equal-angle　interval　sampling　principle.　Compared　with　the　conventional　dq　transformation　detection　method,　this　method　is　on　αβ　reference　frame　and　without　the　phase-locked　loopand　low　pass　filter,　and　the　active　component　of　fundamental　positive-sequence　current　can　be　obtained　exactly　and　quickly.　At　last,　the　efficiency　and　feasibility　of　the　method　is　proved　by　simulation　and　experimentation.　©　2017,　Harbin　University　of　Science　and　Technology　Publication.　All　right　reserved.