<p>To address the complex dynamic behaviors caused by the large gap between the drill string and the wellbore wall and the significant stiffness difference between the upper drill string section and the bottom hole assembly (BHA) in deep and ultra-deep wells, a mapping relationship was established between the actual drill string and the experimental model based on the similarity criterion. By constructing two sets of experimental systems corresponding to the actual wellbore diameters of 444.5&#xa0;mm and 241.3&#xa0;mm, the dynamic behaviors of the drill string under different weights on bit (WOB) and rotational speeds are studied. The experimental results show that the displacement distribution range of the drill string in large-diameter wellbores is much larger than that in conventional wellbores. Moreover, due to the low stiffness of the upper drill string section, its lateral movement shows a high degree of randomness and is more sensitive to changes in rotational speed. The intensity of system vibration is non-uniformly distributed, the lateral vibration was most intense at the upper drill string section and the axial vibration was the greatest at the drill bit. Stabilizers exhibit a significant damping effect. The wellbore diameter significantly alters the influence mechanism of the WOB on vibration. Increasing the WOB can effectively suppress vibration in small-diameter wellbores, but in large-diameter wellbores, it instead leads to an increase in the mean value and fluctuation range of vibration. The dynamic response of the WOB in large-diameter wellbores is intense, and the rock-breaking torque and WOB fluctuations increase significantly with parameter enhancement, being approximately 3 to 4 times that of conventional wellbores. The research results reveal the unique dynamic behavior of the drill string in large-diameter wellbores, providing experimental evidence for drilling parameter optimization and drill tool failure prevention and control.</p>