2D　materials　such　as　graphene　and　transition　metal　dichalcogenides　exhibit　novel　electrical　and　optoelectrical　properties,　which　are　promising　for　the　application　in　sensing　and　imaging.　However,　the　photoresponse　ability　of　pure　monolayer　graphene　in　room　temperature　and　ratio　of　I-ph　and　I-dark　are　still　unsatisfactory,　due　to　the　weak　light　absorption　itself,　short　lifetime　of　photo-excited　carriers　and　large　dark　current,　especially　in　the　infrared　range.　Here,　we　successfully　constructed　a　broadband　graphene-based　phototransistor　consisting　of　lateral　MoS2-graphene-MoS2　heterostructure　by　chemical　vapor　deposition　technique.　It　shows　broadband　photodetection　and　a　low　dark　current　less　than　1　pA　at　applied　bias　of　0.5　V,　resulting　in　excellent　specific　detectivity　more　than　10(12)　Jones　and　nearly　10(9)　Jones　in　visible　and　infrared　band,　respectively.　Moreover,　the　ratio　of　I-ph　and　I-dark　could　be　modulated　by　the　back-gate　voltage　when　the　phototransistor　is　under　the　infrared　illumination.　And　a　high　ratio　of　10(5)　was　exhibited.　This　type　of　graphene-based　phototransistor　by　chemical　vapor　deposition　demonstrates　an　approach　for　the　room　temperature　broadband　photodetection　of　monolayer　graphene　by　energy　engineering.　All　the　results　address　key　challenges　for　broadband　detection　by　graphene-based　phototransistor,　and　are　promising　for　the　large　scale　fabrication　and　integration　in　the　future　electronic　and　optoelectronic　applications.