For the restitution behavior between the tennis strings and the ball, the setting unit which can set up the interval length and tension force of the string is produced, and identified the viscoelasticity characteristic of string side and ball by compression, vibration and impact tests experimentally. It was found that the restitution coefficient is increased with the increasing distance of string interval, but reduced with the increasing string tension at the impact velocity of 5.42m/s. The regularity about the viscosity characteristic is not very much obvious. Furthermore, the influences on restitution behavior are discussed by numerical simulation analysis. The simulation results are not only corresponded with the experimental results, but also revealed that string rigidity is great effective on restitution coefficient. The effect of viscoelasticity can be ignored due to its slight influence.