In order to improve efficiency of query processing while exploring the parallelism, according to the features of asynchronous parallel query processing model in parallel object-oriented databases, three parallel query optimization strategies are proposed, They are: (1) the data subset preselection strategy; (2) the information flow delayed strategy; (3) the information flow reduced strategy. They are suitable for not only the single query but also the multiple queries. The simulation results show that they are efficient practical parallel query optimization strategies.