Abstract: The mode condition of elastic waves in solid-fluid rectangle phononic crystals was derived from the restriction condition of elastic waves,and the mode characteristics of elastic waves were studied on the base of the mode condition.The response of defect modes to mode quantum number and rectangular length was calculated by the characteristic matrix method.Some new defect mode structures different from those of 1D non-confined phononic crystals were obtained.Defect modes of the rectangle doping phononic crystals are determined by mode quantum number;the frequency and full-width at halt-maximum of the defect modes are dependent on mode quantum number and rectangular length.