A long-gauge fiber Bragg grating (FBG) sensing technology is studied, and a chain array method is used to acquire dynamic response of beam. The identification of dynamic parameters of vehicle speed, frequency and vibration mode are realized. A single FBG is applied to pre-stressing, and then encapsulated to form a sensor. The measuring range of gauge is enlarged. A T-shaped reinforced concrete beam with the span of 4 m is equally divided into 8 cells. Sensors with length of 500 mm parallel to the natural axis, and they are independently installed in each cell, which can realize the overall monitoring of beam. The moving load testing is carried out when we use wheeled machine with additional weight. The location and passing time of the wheeled machine are determined when we analyze the time history curve of central wavelength based on the principle of time difference location method, and then the velocity identification is realized. The free vibration of the beam is excited by a vibration exciter. The dynamic response signal is acquired by long-gauge FBG sensors and piezoelectric accelerometers installed on the top of beam. Frequency and vibration mode are obtained by frequency-domain analyzing. The results show that the identification of frequency and vibration mode is achieved by chain array method, and the order of vibration mode identification depends on the gauge length of single sensor.