The　printing　ink　on　the　plastic　surface　will　greatly　reduce　the　quality　of　recycled　plastic　products.　In　this　work,　quaternary　ammonium-modified　waste　cooking　oil　(WCOEQ)　was　fabricated　using　waste　cooking　oil,　epichlorohydrin,　and　trimethylamine　aqueous　solution　as　raw　materials,　through　ring-opening　esterification　and　quaternary　amination　reaction.　The　synthesis　conditions　of　WCOEQ　were　optimised,　and　the　structure　and　properties　of　WCOEQ　were　characterised　by　Fourier　transform　infrared　spectroscopy,　zeta　potential,　and　H-1　NMR.　Furthermore,　WCOEQ　had　excellent　emulsifying　performance,　low　kraft　point,　low　critical　micelle　concentration　value,　good　foaming,　and　stability,　which　could　effectively　reduce　the　surface　tension　of　water,　showing　application　potential　in　the　field　of　plastic　deinking.　Importantly,　compared　with　the　waste　cooking　oil　without　deinking　effect,　the　WCOEQ　had　an　excellent　deinking　performance　on　the　ink　on　the　plastic　surface,　and　the　deinking　efficiency　could　be　improved　by　increasing　the　concentration　of　the　deinking　agent,　the　deinking　temperature,　and　prolonging　the　pre-soaking　and　stirring　time.　The　results　of　atomic　force　microscope,　energy-dispersive　spectroscopy,　optical　photos,　and　Leica　microscope　showed　that　the　roughness　changed　significantly　and　the　ink　molecules　were　gradually　peeling　off.　This　work　highlighted　the　potential　of　quaternary　ammonium-modified　waste　cooking　oil　for　excellent　removal　of　printing　inks　on　the　plastic　surface.