Considering Peierls-Nabarro effect, one-dimensional finite metallic bar subjected with periodic field was researched under Neumann boundary condition. Dynamics of this system was described with displacement by perturbed sine-Gordon type equation.Finite difference scheme with fourth-order central differences in space and second-order central differences in time was used to simulate dynamic responses of this system. For the metallic bar with specified sizes and physical features, effect of amplitude of external driving on dynamic behavior of the bar was investigated under initial "breather" condition. Four kinds of typical dynamic behaviors are shown: x-independent simple harmonic motion;harmonic motion with single wave; quasi-periodic motion with single wave; temporal determine dynamic features.