Abstract: The localization precision and reliability of a rail robot system will be negatively influenced by environmental factors like electromagnetic interference, unstable temperature and illumination. For the problems above, a global localization system for rail robots based on the fusion of odometry and landmark pins is designed. An optimal distribution method of landmark pins is also proposed to improve localization robustness by expanding the distribution difference of landmark pins in each segment. The simulation of wheel spin and landmark pin failure, together with the application results of the substation inspection robot, indicate that the localization precision is at millimeter scale while the system is capable of global localization and can deal with environmental interference.