Abstract: Aiming at the nature of mobile Ad-Hoc networks, such as self-organization, limited communication bandwidth, multi-hop communication, limited energy, limited storage and the frequent disconnection of the links, etc, a problem of mobile data query based on caching is formulated and proved to be a NP-complete problem. Then a polynomial approximate algorithm which is called MD is given to solve the problem. The MD algorithm uses greedy strategy to query cache nodes which store the largest amount of new data packets, so as to reduce the number of query and minimize the network transmission delay. According to the approximate algorithm for mobile data query, another algorithm is proposed based on the max ratio of new data packets and unit communicate delay of cache nodes, called MDD. It not only takes the number of new data packets into account, but also considers the quality-of-service of the links. This algorithm can improve the efficiency of query, minimize network data transmission delay, reduce energy consumption and improve network throughput. Theoretical analysis and experimental results indicate that the proposed algorithms can make full use of the data of cache nodes, complete data query better, reduce data transmission delay, as well as improve the efficiency of query efficiently.