The design idea and implement process of water detecting and alarming system which uses SPC exchange net and water detectors is introduced. The system controls the triode’s base voltage using the conductive characteristic of water, controls the relay switching to call alarm center using the switching characteristic of the triode. The alarm center identifies the calling number, and then dials related user to implement voice alarm. Tests show that the system works stably and has good realtime property. The system can satisfy the requirement and provide certain ptomotional value and applied value.