A vehicle-mounted device for preventing vehicle overrun at a tail end of a route, comprising: a positioning module, configured to be connected to a satellite positioning system and configured to acquire a satellite position of a vehicle; a calibration module, configured to carry out positioning calibration for the satellite position according to an actual position of the vehicle when the speed of the vehicle is zero; a speed acquisition module, configured to acquire a current speed of the vehicle in a real time and use the current speed as a computational speed; a calculation module, configured to calculate and obtain a running distance of the vehicle based on the computational speed; calculate and obtain a distance from a vehicle current position to the tail end based on the running distance and a positioning of a starting point of a scheduled route corresponding to the vehicle; and calculate and obtain a braking distance corresponding to the current speed in terms of a preset acceleration value based on the computational speed; a determination module, configured to determine whether a difference value between the distance from the vehicle current position to the tail end and the braking distance is less than a preset safety margin; and a braking output module, configured to be electrically connected to a braking system of the vehicle, and configured to output a braking instruction to the braking system when the difference value between the distance from the vehicle current position to the tail end and the braking distance is less than the preset safety margin; wherein the speed acquisition module comprises: a first speed acquisition unit, configured to be connected to an I/O interface of the vehicle to acquire a current acquisition speed of the vehicle; a second speed acquisition unit, configured to be connected to the satellite positioning system to acquire a current positioning speed of the vehicle; and a computational speed determination unit, configured to use the current acquisition speed as the computational speed when the current acquisition speed is available, and use the current positioning speed as the computational speed when the current acquisition speed is not available. a positioning module, configured to be connected to a satellite positioning system and configured to acquire a satellite position of a vehicle; a calibration module, configured to carry out positioning calibration for the satellite position according to an actual position of the vehicle when the speed of the vehicle is zero; a speed acquisition module, configured to acquire a current speed of the vehicle in a real time and use the current speed as a computational speed; a calculation module, configured to calculate and obtain a running distance of the vehicle based on the computational speed; calculate and obtain a distance from a vehicle current position to the tail end based on the running distance and a positioning of a starting point of a scheduled route corresponding to the vehicle; and calculate and obtain a braking distance corresponding to the current speed in terms of a preset acceleration value based on the computational speed; a determination module, configured to determine whether a difference value between the distance from the vehicle current position to the tail end and the braking distance is less than a preset safety margin; and a braking output module, configured to be electrically connected to a braking system of the vehicle, and configured to output a braking instruction to the braking system when the difference value between the distance from the vehicle current position to the tail end and the braking distance is less than the preset safety margin; wherein the speed acquisition module comprises: a first speed acquisition unit, configured to be connected to an I/O interface of the vehicle to acquire a current acquisition speed of the vehicle; a second speed acquisition unit, configured to be connected to the satellite positioning system to acquire a current positioning speed of the vehicle; and a computational speed determination unit, configured to use the current acquisition speed as the computational speed when the current acquisition speed is available, and use the current positioning speed as the computational speed when the current acquisition speed is not available. a first speed acquisition unit, configured to be connected to an I/O interface of the vehicle to acquire a current acquisition speed of the vehicle; a second speed acquisition unit, configured to be connected to the satellite positioning system to acquire a current positioning speed of the vehicle; and a computational speed determination unit, configured to use the current acquisition speed as the computational speed when the current acquisition speed is available, and use the current positioning speed as the computational speed when the current acquisition speed is not available.