In　the　industrial　automated　production　line,　how　to　use　the　existing　low-cost　pneumatic　equipment　to　obtain　the　best　positioning　effect　has　become　a　significant　engineering　problem.　In　this　paper,　a　differential　switching　method　is　proposed　in　a　pneumatic　servo　system　consisting　of　four　low-cost　on-off　valves　for　more　precise　control　and　lower　prices.　All　valves　are　simultaneously　open　at　the　initial　stage　of　each　control　period,　and　the　differential　closing　time　of　the　desired　valves　is　calculated　through　the　theoretical　models.　A　sliding　mode　controller　is　applied　with　the　proposed　method,　and　the　system　stability　is　proven.　The　real-time　control　setup　including　three　software　layers　is　proposed　to　implement　the　algorithm.　Several　experiments　are　performed　on　a　real-time　embedded　controller.　Average　0.83%　overshoot　and　0.18　mm　steady-state　error　are　observed　in　the　step　response　experiment.　The　highest　frequency　of　sine　wave　that　can　be　tracked　is　1　Hz,　and　the　average　error　is　1.68　mm.　The　maximum　steady-state　error　is　about　0.5　mm　in　the　step　response　under　payloads　of　5.25　kg.　All　the　simulation　and　experimental　results　prove　the　effectiveness　of　the　control　method.