The　tree　structure　based　block　partition　in　H.264　has　been　shown　to　be　more　efficient　than　simple　uniform　block　partition.　However,　tree　based　partition　still　does　not　code　efficiently　enough　with　video　information,　as　it　is　unable　to　capture　the　geometric　structure　of　20　data.　Concerned　with　this　problem,　this　paper　proposes　a　new　motion　compensation　technique　using　polyline　based　block　partition.　A　polyline,　composed　of　two　line　segments,　is　used　to　approximate　the　curve　contour　of　moving　objects.　By　using　polyline　based　partition,　the　accuracy　of　motion　compensation　can　be　improved　and　the　prediction　error　can　be　reduced.　Curvature　analysis　of　object　contour　within　macroblocks　verified　the　validity　of　the　proposed　method.　Experimental　results　show　that　the　proposed　method　improves　the　coding　efficiency　by　0.2-0.3dB　in　PSNR,　when　compared　to　H.264/AVC.