A system structure for two-layer wireless sensor networks (WSN) was designed to meet the requirements of precision irrigation and characteristics of fixed pipeline type sprinkler irrigation system. Through analyzing the relation between sensor's detection radius and sprinkler’s range, two analysis expressions for minimum number of nodes were theoretically educed under circumstances of full coverage in a region. Combining network structure with nodes assignment, a data transmission mode was presented, and data transmission reliability was guaranteed by fault diagnosis with classifying management. The preliminary research indicates that communication via this network is feasible.