Using the continuum limit of SSH model, we find explicitly the "polaron" soliton in one-dimensional Peierls system with commensurability-3. It is shown within the weak-coupling limit that the polaron solution satisfies exactly the self-consistent condition for the order parameter of the ionic displacements. The creation energy and characteristic width of the polaron are given. Furthermore, the possible soliton excitations in the general commensurability-M case are discussed.