The spin stabilized solid-propellant rocket motors have often been used as the final-stage propulsion system in deploying spacecrafts into designated orbits. Nevertheless, the self-spinning of spacescrafts can cause nutation instability during the combustion process of upper-stage rocket motor and may deploy spacecrafts into error orbit. Thus, a scale-down solid rocket is used to simulate real fly condition with the purpose of finding reasons of nutation instability. The result confirms that the modify slag theory is reasonable in the nutation instability analysis.