Abstract: A method for merging document clusters includes the following steps. An association graph among document clusters is established. The association graph is an oriented graph. Each document cluster is represented by one node in the association graph, and each node is searched in a pair-wise manner. An oriented edge is established between any two nodes having associated weights there-between reaching a preset value. An arrow of the oriented edge points to a node capable of serving as a descriptor for the other node. An associated weight is assigned to the oriented edge to represent an association degree between the two nodes. Any two document clusters that can serve as a descriptor for each other and have an association degree there-between reaching a preset threshold value are merged into a single document cluster.