The effects of fuel position on the attitude of spacecraft with elastic appendages were studied under the condition that the fuel sloshes violently and assuming that the coupling system pitches round the mass center of the whole system.The coupling dynamics equations were deduced by using HO principle,the analytical expressions of the natural frequencies of the coupling system were obtained,and the effects of fuel position on the natural frequencies of the coupling system were analyzed. Then the multiple scale method was employed to analyze the primary resonance of the rigidliquidelastic coupling system, which showed that the amplitudefrequency response switches between soft and hard spring type at the critical depth changed with the fuel position, and that, if given the force moment, the multivalue and bifurcation phenomena could occur.