Abstract: The relationship between resonance and surface waves and scattering of an infinite elastic cylinder excited by an obliquely incident acoustic wave is discussed in this article. According to three dimensional normal mode solutions for a free cylinder, the resonant frequencies of cylinder and correpondingly the phase velocity of helical surface waves and their relation to helical angles are obtained. Furthermore, as a cylinder is excited by sound waves in water, the dispersion of phase velocity for helical surface waves with relation to incident angle also could be derived. comparing the results in this article with results in the article of Flax et al, we found that in obliquely incident condition, the resonant modes are basically in agreement with the frequencies of minimum value in curves, of form function. This phenomenon is analogous with the phenomenon in condition of perpendicular incident.