Unusual　quantum　transport　in　a　quantum　dot　coupled　to　two　normal　metal　leads　was　studied　by　applying　microwave　fields.　When　the　strength　of　the　microwave　field　on　the　quantum　dot　(W-D)　was　increased　and　the　strength　of　the　microwave　fields　on　the　two　leads　was　not　changed,　the　main　peaks　of　the　current　increased,　then　decreased　after　W-D　reached　the　[GRAPHICS]　value.　Conversely,　the　sideband　peaks　of　the　current　changed　in　the　opposite　manner.　We　attempt　to　explain　this　unusual　phenomenon.　Results　show　that　the　current　can　be　controlled　in　practical　applications　by　selecting　appropriate　microwave　field　parameters.