Extracting the users expected information from a large text collection based on some query is the aim of a Information Retrieval (IR) system. Now a days Assamese Digital documents are increasing at a huge rate and to collect the information efficiently from them we are in need of an Assamese IR system for retrieving documents. Comparing query and document term on lexical level and the shorter length query implies the problem like word mismatch. Adding additional term with user's query means expanding the query can improve the IR system's performance. The electronic lexical database, WordNet can help identifying the synonymous expressions and linguistic entities that are semantically similar with the input query. Here we present an Assamese IR system based on vector space model and show our result by considering the query vector as the original user's query and the query is extended using the Assamese WordNet synsets.