A train positioning and speed measuring method based on grating array was proposed to solve the monitoring problems of railway and urban rail transit, such as variable operating environment, long monitoring distance and vulnerable to lightning. The ultra-weak grating array with strong anti-electromagnetic interference ability and large multiplexing capacity is used to form vibration sensing network, and the unbalanced Mach-Zehnder interference demodulation method is used to realize the detection of train traveling vibration signal. The accurate positioning of the train is realized by the endpoint detection method based on the short-term energy after the wavelet denoising, and the running speed of the train in the area is calculated by the distance between the adjacent measuring areas and the arrival time difference of the train. An experimental system was set up between Hugong and Yezhihu stations of Wuhan Metro Line 7 for field test to verify the feasibility of this scheme. The experimental results show that this scheme can achieve accurate positioning of the real-time position of the train, with the measuring speed error is ±2 km/h. And after a long time of testing, the system based on this scheme has good reliability and stability.