Two query expansion method based on the Arabic corpuses have been developed. The first represents the local query expansion methods which are the local context analysis and the second represents the global methods which are the similarity thesaurus and comparisons have been conducted to determine the query effectiveness of the method using the global methods and the local ones. The results have shown an advantage of using the cosine measurement. Finally, it has also been shown that the query expansion by using the similarity thesaurus has improved the local context analysis.