To attain the coupling characters of vehicle-borne strapdown 3-axis stable platform,a complete kinematics and dynamics model of 3-axis stabilization platform system was achieved.Kinematics model analysis indicates that the main difference between strapdown stabilization platform and rate gyroscope stable platform lies in information acquisition and control mode.The rate gyroscope platform gets stability using hardware directly,while strapdown platform gets stability based on the software compensation.Dynamics model shows that the nonlinear cross coupling exists not only between vehicle body and gimbals of stable platform system,but also among gimbals each other.The coupling test not only validated the model,but also obtained the cross coupling boundary ranges of each gimbal,which affords a theoretical foundation for the further study of vehicle mounted strapdown 3-axis stable platform system.