An approximate algorithm for median query（AAMQ） based on WSN was proposed.In AAMQ

each node could estimate the value of the distinct number

and created a subsequence samples which get K percent of the most com-monly used values in its own observed values

and then broadcasted its subsequence to the parents.Finally

these samples were combined to a single sample in the root node which its data structure was far smaller than the size of the whole data set.The approximate value for median query could be introduced from the sample quickly.Experimental results show that the proposed algorithm can greatly reduce the communication

has the advantages of low error range

and is able to significantly prolong system life.