It is essential to monitor the resin injection process of Resin Transfer Molding (RTM) for manufacturing large integrated co-cured structures. This paper discusses the efforts in developing fiber Bragg sensors for monitoring the flow of the resin during the infusion process. Three Fiber Bragg Gratings (FBG) sensors are put into the composite layers at different location, one is used to monitor the temperature and the two others are used to detect the arrival of the resin flow front. The experimental results show that the arrival time of the resin flow front to the No.1 and No.2 sensor are 50 min and 115 min, respectively. The injection end time is 166 min at the maximum temperature of 24.59 ℃. The network of FBG sensors would be very useful to provide information of resin injection of RTM procession.