I n this paper, we address the problem of query processing o n distributed semi-structured data. The distributed semistructured data can be modeled as a rooted and edge-labeled graph, where nodes are located in a single or a number of sites. For eficient retrieval of distributed semi-structured data, we propose a query processing model that is based on the ‘query reduction and diffusion’ method. In the method, a user query is reduced in a site and distributed to other sites for data retrieval. W e also propose a set of algorithms for the proposed model.