Abstract: Fiber grating coupler (FGC) has good wavelength selection characteristic of optical fiber grating as well as multiport advantage of fiber coupler. These features make it easy to realize allfiber optical add/drop multiplex (OADM).Now there are four major types of FGCs: separated structure based on Mach Zehnder interferometer, dissymmetric structure based on 100% coupler, dissymmetric structure based on 0 coupler and symmetric structure based on 100% coupler. The structure, operation principle and present situation of the symmetric structure FGC are introduced emphatically. The test method for the device is proposed. Furthermore, the application of this device used in largescale WDM optical fiber sensor arrays was also investigated.