Abstract: As a representative acoustic system，band structure of a periodical string-ball chain has been widely studied.In spectrum measurement，it^,s noteworthy that a novel，robust class of eigenstates (edge states)，whose energy lies in the band gap and wave function locates at the edge of the system，have been detected.In this paper，the resemblance between the experiment-observed edge states and ones in topological insulator enabled to develop an analogous theory of topological acoustics to study string-ball system.Numerical simulation of topology invariants demonstrates non-trivial topological properties of the experiment system，proving that the observed edge states are topological-protected edge states；Based on numerical results，a brief discussion is given on topological phase transition and transport properties of edge states.

Key words: edge state, topological invariants, topological phase transition, transport properties