The invention discloses a vehicle-mounted strapdown inertial navigation system. The system is a core component composed of a laser gyro, an accelerometer, a barometric altimeter, a speedometer and other sensors and provides high-precision autonomous positioning and directional guidance. The system is good in concealment, the working environment is not disturbed and influenced by the outside and isnot limited by meteorological conditions, the system has the advantages of autonomy, concealment, real-time performance, all-weather performance and the like, and accurate position coordinates, azimuth angles, roll angles, pitch angles, speeds, travelled distances, heights and other information of carriers can be provided in real time. The system is suitable for navigation, guidance, positioningand orientation, attitude control and the like of various carriers.