An　improved　discrete-time　approach　is　proposed　for　modeling　a　class　of　switching　converters　which　have　non-invertible　coefficient　matrixes　in　state　equations.　In　the　form　of　block　matrix,　the　proposed　approach　is　generally　derived　by　using　the　linear　relation　between　the　derivatives　of　two　blocks　in　state　equations.　A　filter　converter　example　is　provided　to　illustrate　the　effectiveness　of　the　proposed　approach.　Our　work　perfects　the　discrete-time　approach　in　modeling　and　analyzing　of　switching　converters,　so　engineers　can　deal　with　more　practical　system.