A novel liquid refractive index (RI) wireless sensor network based on long period fiber gratings (LPFGs) and ZigBee is presented. The system includes sensor node, router node, coordinator and computer. In the sensor node, a kind of low-cost LPFG sensor based on the light intensity modulation is designed to measure liquid RI, which is made up with LPFGs and a special fabrication. At the same time, driver board of sensor is designed, which is made up with laser diode and photonic diode. Because of the nearly linear sides of loss peaks, the light power at one side of half of loss peak at fixed wavelength is measured to monitoring RI. A system is established by Zigbee, and realizes real- time, multi- point RI monitoring. NaCl solution, which has the RI range from 1.3347 to 1.3418, is measured. The resolution of RI is 0.0001, the maximum error of the sensor is 0.0004, and the average error is 0.00015. The system provides a new solution for applying optical fiber sensors to wireless network. It is convenient to set low- cost sensor network in large area and remove or add sensor nodes, and it has realized large-scale, multi-point, and high resolution environmental monitoring.