1. A method comprising: receiving a plurality of search key word sets that were previously input by a plurality of users; obtaining category information corresponding to the plurality of search key word sets, the category information being determined based at least in part on the plurality of users' selections; segmenting each of the plurality of search key word sets into search key word units; determining a plurality of importance levels of the search key word units, wherein determining the plurality of importance levels includes: determining, based on recorded log information, a plurality of unique visitor (UV) quantities for the plurality of search key word units under corresponding categories; and determining a plurality of importance levels of the search key word units includes determining category entropy; and determining category entropy for each of the plurality of search key word units under its corresponding categories, wherein the category entropy is determined by: H i = ∑ j = 1 K ⁢ ⁢ ( - P ij P i ⁢ log 2 ⁢ P ij P i ) , wherein, H i is the category entropy of search key word unit i; wherein K is the quantity of categories where UVs for the search key word unit i are rep sent; wherein P ij is the UV quantity for the search key word unit i in the j th category; wherein P i is the UV quantity for the search key word unit i in all pieces of category information; combining the search key word units into a plurality of search key word unit groups that correspond to a plurality of stages, the search key word unit groups corresponding to the same stage having the same number of search key word units; based at least in part on the category information corresponding to the plurality of search key word sets, determining category information that specifically corresponds to the plurality of search key word unit groups; and based at least in part on category information specifically corresponding to the plurality of search key word unit groups, establishing a plurality of search key word tables corresponding to the plurality of stages, each stage having a corresponding search key word table that comprises the correspondence between the search key word unit groups for said each stage and the category information that specificallys correspond to the plurality of search key word unit groups; wherein: the plurality of search key word tables are used to provide current category information of a current search key word set input by a user.