During terminal-sensitive rocket bomb launching in cylinder, mass and mass center position change over time. In order to analyze the law of motion during launch, the dynamic model of motion of rocket bomb in cylinder in the constraint period was established by Kane method and simulated by Simulink. It was concluded that the variation law of rocket bomb space position and attitude was simulated with certain falling velocity, rotational speed and scan angle. In the progress, the variable quantity of steady scan angle is proportional to initial scan angle and inversely proportional to mass flow rate of rocket engine. In addition, randomness of thrust eccentric direction causes scatter of scan angle.