Dynamic Poisson’s ratio is a very important parameter for the numerical analysis of dynamic responses in a rock-fill dam. It is generally taken as a constant of which the significance is generally underrated. In order to have a better understanding of the dynamic properties of rock-fill materials, a series of tests were performed to investigate the effects of the shear strain on the dynamic Poisson’s ratio. The experimental results show that dynamic Poisson’s ratio varies with the shear strain, the dynamic shear modulus and the confining pressure. In addition, the empirical formulas to determine the dynamic Poisson’s ratio with the shear strain or normalized shear modulus are given in this paper.