Abstract: In this paper attitude dynamics of liquid-filled spacecraft with elastic appendagesis studied- Motional equations of liquid, motional equations of system and motionalequations of particle of elaJstic plates are obtained by using the theorem of angu-lar momentum, the conservation law of angular momentum and Newton's motionallaw. When elastic plates deploy at uniform velocity of plates motional equationsof plates are alternated. Using Runge-Kutta method, the plate's amplitudes ofvibration are obtained. Using motional equations of system,the attitude angularvelocities of spacecraft are obtained.