Framework　modification　of　graphitic　carbon　nitride　(g-C3N4)　with　organic　molecules　is　recognized　as　an　effective　strategy　to　enhance　its　photocatalytic　performance　by　improving　the　charge　separation　in　g-C3N4.　In　this　work,　pyromellitic　diimide　(PD)　with　strong　electron-withdrawing　ability　and　conjugated　structure　was　linked　to　g-C3N4　skeleton　by　simple　solution　blending　to　prepare　a　composite　of　g-C3N4@PD.　It　is　found　that　the　resultant　composite　exhibited　much　higher　photocatalytic　activity　than　pristine　g-C3N4　in　the　photodegradation　of　an　anionic　dye　of　sulforhodamine　B　(SRB).　Specifically,　the　composite　with　PD　of　1%　in　weight　ratio　showed　a　degradation　rate　constant　3.8　times　and　5.1　times　that　of　g-C3N4　under　the　illumination　of　visible　light　and　ultra　violet　light,　respectively.　Moreover,　g-C3N4@PD　revealed　highly　selective　photodegradation　in　favor　of　a　cationic　dye　of　malachite　green　in　its　mixture　with　the　anionic　dye　of　SRB,　which　is　attributed　to　preferential　adsorption　of　the　cationic　dye　onto　the　negatively　charged　photocatalyst.　In　addition,　the　composite　maintained　a　high　photodegradation　efficiency　of　98.2%　at　the　end　of　five　cycles　of　the　photodegradation　of　SRB,　suggesting　good　photocatalytic　stability.　It　is　proposed　that　enhanced　photocatalytic　activity　of　the　composite　is　related　to　the　electron-withdrawing　effect　of　PD,　which　facilitates　the　separation　of　photo-induced　electrons　from　the　g-C3N4　skeleton　to　the　boundary　PD　to　inhibit　the　recombination　of　the　photogenerated　electron/hole　pairs　in　g-C3N4　skeleton.　The　facilely　prepared　g-C3N4@PD　is　a　promising　photocatalyst　in　environmental　remediation.