Abstract: The theory and experiment about gravity waves in arectangular elastic fluid-shell coupled system are presented in thispaper. A set of equations are constructed according to fluid and vibrationtheory. Based on the boundary and initial conditions of the system, thevelocity potential of the fluid and the surface wave function of the firstgravity wave are obtained. Through the numerical calculation for theequations, the time response curves and response spectrum are given to thefirst gravity wave. The results show that when gravity wave appears, theshell acts as pendulum and the gravity wave's motion is harmonic.Furthermore, the effects of exciting force and the frequency to the systemare also discussed. Only when the force is large enough to conquer theviscid resistance and the frequency is near a certain constant, gravitywaves are engendered, which is the result of resonance vibration. At thesame time, the experimental study is processed. The phenomena observed areresonance without gravity wave if the system is excited on the shell with ahorizontal force and the force is large enough but the frequency out of thescope. When all the conditions are met, large-amplitude and low-frequencygravity waves are observed. All the experimental results show goodqualitative agreement with the theoretical results.