Due to the lack of users knowledge of the collections used by search engines and in general retrieval systems, users can not express their information need appropriately in queries. In other words, they do not have enough experience to formulate their needs to find related documents. The idea of user’s query expansion aims to help users to improve and correct the queries. In fact, retrieval system, regarding the feedback it receives from user at the first stage, moves the query in set space to more related documents. Different approaches in information retrieval systems have been used; however, there has not been any assessment of efficacy of query expansion in Farsi information retrieval systems. In this paper, expansion of basic model of Rocchio, assessed as the primary model to retrieve Farsi documents, has been presented. As a matter of fact, the purpose of this study is to determine the effect of a standard and basic model on query expansion to retrieve Farsi documents, so that the researchers can compare their achievements of query expansion with the findings of this paper which showed a straightforward and positive effect on Farsi document retrieval.