In　traditional　cloud　computing　system,　searchable　encryption　is　deemed　as　a　core　technology　to　realize　data　confidentiality　protection　and　information　retrieval　functions.　However,　the　online　payment　problem　and　mutual　distrust　between　cloud　platforms　and　users　may　hinder　the　wide　adoption　of　cloud　service.　In　this　paper,　we　construct　a　blockchain　based　multi-keyword　ranked　search　with　fair　payment　(BMFP)　system,　which　leverages　smart　contracts　to　verify　the　correctness　and　completeness　of　the　search　result,　and　automatically　execute　the　fair　payment　operations.　The　system　realizes　public　verifiability　on　a　multi-keyword　ranked　search　result.　The　data　owner　manages　the　search　authority,　and　a　concrete　fair　payment　smart　contract　is　designed.　The　BMFP　is　compatible　with　Ethereum,　and　the　verification　algorithm　executed　by　the　smart　contract　is　cost-efficient.　©　2013　IEEE.