Drillstring in oil drilling is simplified as a half-infinite bar. Taking account of Peierls-Nabarro(P-N) force and viscous effect of solid, dynamic response is simulated under harmonic driving at the end of the bar. With the physical properties specified, periodic, quasi-periodic and chaotic motions would appear as a function of the amplitude of external driving. We find that all the particles of the bar have the same qualitative characters, while vibrating amplitude decreases along the bar. It appears that particles of the bar reach chaotic motion through quasi-periodic motion. Investigation of this half-infinite bar will provide references for design of drillstring to keep motion away from chaotic region.