Maleic　anhydride　grafted　high　density　polyethylene　(HDPE-g-MAH)　was　prepared　by　UV-irradiation.　Factors　of　the　irradiation　time,　monomer　content,　initiator　content,　and　styrene　as　a　co-monomer　on　the　grafting　rate　and　gel　content　of　HDPE-g-MAH　were　studied.　The　results　show　that　the　optimal　duration　of　UV-irradiation　is　30s.　The　grafting　rate　increases　with　MAH　content,　while　the　grafting　efficiency　increases　up　to　5.2%　MAH,　where　it　drops.　The　content　of　benzophenone　(BP)　affects　greatly　the　grafting　rate　and　gel　content,　and　the　optimal　BP　content　is　0.5%.　Adding　styrene　into　the　graft　system　reduces　apparently　the　gel　content　of　HDPE-g-MAH.