In　lately　published　video　coding　standard　Versatile　Video　Coding　(VVC/　H.266),　the　intra　sub-partitions　(ISP)　coding　mode　is　proposed.　It　is　efficient　for　frames　with　rich　texture,　but　less　efficient　for　frames　that　are　very　flat　or　constant.　In　this　paper,　by　comparing　and　analyzing　the　rate　distortion　cost　(RD-cost)　of　coding　unit　(CU)　with　different　texture　features　for　using　and　not　using　ISP(No-ISP)　coding　mode,　it　is　observed　that　CUs　with　simple　texture　can　skip　ISP　coding　mode.　Based　on　this　observation,　a　fast　ISP　coding　mode　optimization　algorithm　based　on　CU　texture　complexity　is　proposed,　which　aims　to　determine　whether　a　CU　needs　to　use　ISP　coding　mode　in　advance　by　calculating　CU　texture　complexity,　so　as　to　reduce　the　computation　complexity　of　ISP.　The　experimental　results　show　that　under　All　Intra　(AI)　configuration,　the　coding　time　can　be　reduced　by　7%,　while　the　BD　rate　only　increase　by　0.09%.　©　2021,　The　Author(s).