Abstract: Examined in this paper is the issues of on-line maintenance for growing text collections. This approach builds inverted index to reflect changes in the collection it describes, supporting efficient document insertions and deletions. A fast on-line index construction method based on dynamic balancing tree is proposed. This method takes a merge-based approach and aims to keep a good performance during indexing and query processing by always merging indices with similar sizes. This is achieved by using a tree in which each node corresponds to one sub-index. The placing of sub-indexes in the tree depends on the sizes of the sub-indexes, so that each merging takes place among similarly sized sub-indexes. The method is suited very well not only for growing text collections, but also for dynamic text collections, and is a uniform framework for merge-based index maintenance strategies. It is more general, faster and scales better than previous methods, and can be adapted to suit different balances of insertion and querying operations. Using experiments on large scale Web data, the efficiency, flexibility and scalability of this method are demonstrated in practice, showing that on-line index construction for growing text collections can be performed efficiently and almost as fast as for static text collections.