Abstract: The Speed Measurement and Positioning System based on speed sensor is widely used in railway transit field. This article introduced the principle and algorithms for speed measurement, referenced the train speed measurement accuracy and the typical parameters of resolution ratio provided in Appendix 3 of the IEEE 1474.1 Standard, analyzed the value condition of system parameters which could provide a reference for system designers while the speed measurement accuracy and resolution ratio were set. Through the study on the structure of common Speed Measurement and Positioning System, the article given the positioning algorithms based on the speed sensor, explained the factors affecting the positioning error briefly, put forward improvement measures for reducing the error of speed measurement and positioning.