Mining association rules are an important data mining problem. In this paper ,an association rules mining algorithm,ARDBSO,which is based on set operation,is given. It can find all large itemsets in the database while only scan the database once. So,the time for I/O is reduced enormously and the efficiency of ARDBSO is improved. The experiments show that the efficiency of ARDBSO is 80~ 150times of Apriori's.