A novel practical cooperative diversity method for power-limited wireless sensor network system was proposed.At first, the system model was presented and the cooperation problem is formulated under the minimum outage probability criterion, then the focus was put on the power efficiency of system, such as the relay selection,cooperation strategy and power allocation etc.At last the uniform procedure of the proposed method was given.The results of the simulation clearly demonstrate that our method not only has the properties of simple operation and wide applying scope, but also outperforms those of current classical methods on the aspect of outage probability under the basis of the same power limitation.