Generally,　the　key　determining　the　converter＇s　performances　is　what　control　strategy　is　selected　and　how　to　implement　the　control　law.　The　one　cycle　control　method　proposed　in　recently　year　is　a　kind　of　nonlinear　control　strategy　which　possesses　fast　response　on　line　voltage　vary　and　can　eliminate　the　effect　on　the　output　voltage　due　to　the　disturbance　of　the　line　voltage.　But　the　drawback　of　this　control　method　is　slow　response　on　load　vary.　A　new　open-loop　nonlinear　control　strategy　based　on　equivalent　controlled　source　average　method　is　proposed　in　this　paper.　The　new　open　loop　control　method　can　eliminate　the　effect　on　the　output　voltage　of　PWM　DC/DC　converters　due　to　the　large　and　small　signal　disturbances　of　the　line　voltage　and　the　load.　The　buck　circuit　was　taken　as　a　example　to　explain　the　new　control　method.　First,　the　average　large　signal　low　frequency　circuit　model　is　set　up.　The　new　open　loop　nonlinear　control　strategy　is　constructed　by　analysis　the　average　buck　circuit　model.　It　is　found　that　the　new　open　loop　control　method　can　eliminate　the　effect　on　the　output　voltage　due　to　the　large　and　small　signal　disturbance　of　the　load.　The　control　method　can　get　the　excellent　performances,　inherent　stability,　fast　response　and　no　overshoot.　In　order　to　realize　the　control　method,　the　mathematical　model　of　inductor　voltage　low　frequency　content　is　set　up.　Computer　simulation　and　experimental　verification　of　the　described　control　strategy　was　performed.