The existing security systems show many shortcomings such as difficult to extend and severe time-consuming because it is based on wiring network technology. In this paper, we present a wireless networked security system based on ZigBee technology. The system adopts hybrid topology structure based on cluster, which consists of many micro-sensor nodes, network coordinator nodes, network gateway (router), communication network and monitor centre (computer). For short distance transmission, the micro-sensor nodes collect data from the monitoring surroundings and transmit to the gateway using ZigBee communication. For long distance transmission, from the gateway to the monitor centre, system uses TCP/IP protocol. The gateway in this system is the protocol conversion used to transform a data package in ZigBee protocol to TCP/IP protocol before transmitting. A modified routing protocol based on LEACH is adopted in the system. The simulation result shows that the modified LEACH protocol has superiority on survival time. The wireless micro-sensor can be scattered to the surroundings that human unable enter. Then the sensor nodes self-organizing networked security system and realize security monitor task. The system also can be used to forest fireproofing and environment pollution inspection after modification.