The fiber Bragg grating (FBG) sensor network which is used to monitor the external load position information of a certain aircraft wing box is researched in this paper. The forecast precision influence of the disabled sensor number to the external load position information is researched; Optical switch is introduced to overcome the shortcoming of the traditional FBG sensor network topology low reliability, proposing a higher reliabile network topology, and the reliability of the two types FBG network topologys are researched. The results indicate that the reliability of the new sensor network is superior to the traditional one obviously. The reliability of the two types network topologys is dependent on the failure rate of the single sensor. When the single component failure rate change between 0.001 and 0.01, if the acceptable position forecast error of the external load is less than 5 mm, the failure rate of the new sensor network is reduced to 50% of the traditional one; if the acceptable position forecast error of the external load is less than 10 mm, the failure rate of the new sensor network is reduced to 12.5% of the traditional one at least.