The mechanical properties of the rotary drilling system are analyzed in depth and the complex mechanical behaviors of integral tubular strings and the effects of joints are studied. The results show that before the mechanical calculation of the drilling string, the inversion of the friction coefficient by the near-well data can improve the calculation accuracy of the friction and torque of the string. Rotating casing can ensure smooth running in the extended well. The injection of light medium can alle­viate the axial force, but it is not enough to ensure safe running, which needs to be combined with the rotating casing method. By increasing the rotation per minute and reducing the weight on bit, the buckle of drill string can be avoided.