Abstract: Recognizing the contact nonlinearity between drillstring and borehole, the finite element iterative method is used to calculate the dynamic characteristics of drillstring, such as whirl speed, whirl orbit, lateral and axial accelerations. Furthermore, the effects of rotary speed on dynamic characteristics of drillstring are analyzed. The results show that high acceleration and frequency impact between drillstring and borehole wall may lead to whirl and chaotic motion, and increase the alternating stress. These severe vibrations may result in premature drillstring failure and damage to the downhole tools. By rotary table speed optimization, drillstring vibrations can be reduced and the dynamic stress can be controlled at a low level. The results are helpful to engineering applications and provide theory supports for drilling operations.