Ultra-deep sidetracked horizontal wells are widely used in the efficient exploitation process of unconventional oil and gas resources. Their narrow spatial dimensions and horizontal spatial orientation easily lead to dynamic contact between the drill string and the wellbore, thereby affecting the dynamic behavior of the drill string. In response to the aforementioned engineering issues, by analyzing the motion and mechanical characteristics of the drill string at the contact point with the wellbore, a dynamic model of the drill string for ultra-deep sidetracked horizontal wells was built, and the reliability of the model's simulation results was verified through physical experiments. Secondly, based on actual drilling cases, the constructed model was used to simulate and analyze the three-dimensional displacement of the drill bit, the three-dimensional velocity distribution, the three-dimensional load distribution of the drill string, and the impact of rotation speed on the vibration of the drill string. The research results Show as follows. Compared to traditional drill string dynamics models, the newly developed model incorporating dynamic contact characteristics between the drill string and wellbore better aligns with the requirements for drill tool safety analysis and wellbore trajectory control in ultra-deep sidetracking horizontal wells. During the drilling operation of the sidetracked horizontal well, the transverse vibration of the drill bit exhibits a significant harmonic state, and this vibration state causes the drill string to undergo a larger longitudinal displacement. There is a coupled response relationship between the transverse and longitudinal vibrations of the drill string, with the longitudinal vibration intensifying the transverse vibration amplitude by increasing its own curvature. The vibration loads of the drill string are mainly concentrated in the lower structure and decay rapidly during propagation upwards. Rotational speeds within the ranges of 195.00 ~210.00 r/min and 100.00 ~ 140.00 r/min during sidetracking horizontal well drilling operations are prone to cause bit damage, wellbore enlargement, and drill string fracture, thus requiring avoidance in practical applications.