As the Low Earth Orbit (LEO) satellite constellation becomes more mature, LEO for vehicle localization could be a supplement or a replacement in challenge situations of traditional Global navigation satellite systems (GNSS). This paper designs a dedicated LEO satellite simulator for vehicle localization, which also integrates with IMU for more precise localization. The simulator includes satellite trajectory generation, observable satellite identification, vehicle localization solver, and an Extended Kalman Filter (EKF) sensor fusion strategy for more precise localization. The LEO simulator was also seamlessly integrated with the Carla simulator for vehicle localization assessments. Comprehensive tests were conducted with the simulation tools to evaluate LEO satellite -based vehicle localization performance across different satellite counts. Furthermore, the capability and reliability of the developed LEO simulator are verified by the experimental data. Both simulation and experiment results indicate the potential of LEO satellites for precise and reliable vehicle localization for automated driving. Additionally, the designed simulator offers a versatile platform that is flexible to integrate with other satellite simulators or other sensors' measurements, like LiDAR and camera, for precise localization or other usages.