The　mass　transfer　in　catalyst　capsule　is　analysed.　It　is　pointed　out　that　the　wetting　incompletion　of　catalyst　beads　and　the　concentration　gradient　within　the　catalyst　capsule　reduce　catalyst　efficiency.　The　effectiveness　factor　of　catalyst　capsule　equals　to　the　product　of　ηx　and　ηc.　The　former,　the　effective　wetting　rate　of　catalyst　beads,　represents　the　influences　of　wetting　incompletion　of　catalyst　on　catalyst　efficiency,　the　latter　represents　that　of　concentration　gradient.　A　two-dimensional　model　is　established　and　an　equation　to　calculate　ηc　is　given.　It　is　indicated　that　ηc　is　influenced　not　only　by　radial　diffusion,　but　also　by　axial　liquid　flow.　The　influence　of　diffusion　resistance　on　effectiveness　factor　is　greatly　weakened　by　axial　liquid　flow.