Abstract: This paper is to study and control the dynamic characteristics of drillstring in a straight hole. The stress and deformation of drillstring is analyzed and a dynamic model of drillstring is established. The dynamic characteristics including whirl orbit and whirl speed of drillstring are studied through finite element method. The whirl speed at depth 5256 m reaches 252 r/min while the table rotary speed is only 120 r/min. The stress fluctuation at depth 261-732 m rises up to 15 MPa. The results show that the stress fluctuation in drillstring is the major factor for drillstring failure, and the control of the drillstring dynamic stress is important to minimize the drillstring failure.