The existing rail transit location and speed measurement method is easy to be interfered by the external environment and has instability. In order to solve these problems, based on the fiber grating with the characteristics of insulation, strong anti-interference, and corrosion resistance, a high precision train speed measurement and location system based on weak grating array combined with wave division and optical time-domain reflectometer (OTDR) technology was proposed. The absolute location requirement of grating points was realized by intensive multiplexing, and a data processing method was designed to calculate real-time speed and position according to the location results of different grating partitions and their wavelength drift rules. In order to verify the performance of the system, a simulated operating environment was built. And theoretical analysis and experimental verification were carried out. Experimental results show that centimeter-level positioning accuracy and 1 km/h speed measurement accuracy can be achieved with the proposed scheme, which has a wide application prospect in rail transit.