Set is a common data type in database system today．But there is no efficient index structure for set type data to support the queries relate to it．This paper presents a structure called SetUie．The stlxlcture is built based on the common prefix patterns in database．Unlike invert file，the sets with salne value are well organized．So the size of the data accessed by a query is smaller than that of invert file．This feature will cause the improvement of the selection operation’s performance．The experiments support this result．In this paper We also discuss several eptimizations approaches to Settrie．