This paper investigates the query processing in mobile Ad Hoc wireless networks. A cost evaluation model for join operations is presented, which evaluates the primary parameters of wireless networks, including the size of the transmitted data, the transmission distance and the query cost at each local node. A join processing algorithm is also proposed in this paper. Given a multi-join query, our algorithm will first decide how to transmit data among the referenced nodes, then determine the optimal join order with minimal cost. Theoretical analysis and experiment results show that the proposed method is much more efficient.