In order to reduce the algorithm complexity of the target coverage problem in Wireless Sensor Network(WSN),three approaches are designed to decrease the network scale.Of the three approaches,one is deleting the redundant sensor nodes,another is removing the redundant targets,and the third is decomposing the target-coverage graph into independent sub-graphs.It proves that the three approaches are correct,and presents the Construct Independent Sub Graph Algorithm(CISGA) to divide target-coverage graph.Measurement results show that CISGA can r...