Abstract: As drilling depths increase, the mechanical problems involved in drilling string motion become more complicated. The simulation and analysis of dynamic characteristics of drilling strings could contribute to safe, high-quality, and efficient drilling. In order to explore the motion characteristics of drilling strings in extra-deep wells, the governing equation of drilling string motion was time-discretized using the Newmark method, and the successive over-relaxation (SOR) node iteration method was used to solve the entire configuration of the drilling string at each time step. The dynamic characteristics of the drilling string with a total length of over 9 000 m were simulated. The whirl trajectory, whirl velocity, and lateral acceleration of the drilling string at four typical positions were given. The whirl and stick-slip characteristics of the drilling string were also analyzed. The results demonstrate that the whirl and stick-slip phenomena in the upper part of the drilling string are not obvious and that as the position moves down, irregular whirl and insufficient stick-slip phenomena appear, and the drilling string near the bit may experience violent whirl and stick-slip vibration. The drilling string near the neutral point has the most violent whirls and serious friction, which may bring potential safety risks to the drilling string. The research results can provide theoretical basis for the safe drilling of extra-deep wells.