Background/Introduction <p>Large friction in ultra-long horizontal wells and extended-reach wells poses significant challenges to drilling efficiency and cost control. Oscillation drag reduction technology has been developed to alleviate these friction-related issues.</p> Purpose <p>To address this problem, a new double-piston oscillation drag reduction tool (DPOT) is proposed, and its influence on drill string dynamic behavior is investigated.</p> Methods <p>Using the equivalent mass and lumped-parameter method, a coupled longitudinal–torsional–transverse dynamic model of a drill string system incorporating the DPOT is established. The vibrational responses of the drill string and bit are analyzed under different input flow rates.</p> Results <p>The results show that increasing the input flow rate leads to a higher longitudinal vibration displacement amplitude and increased vibration frequencies, while the torsional speed and transverse vibration amplitude vary only slightly. The stabilized longitudinal vibration amplitude at the bit is larger than that of the upper drill string but shows limited sensitivity to flow rate. After using the DPOT, the stabilized transverse vibration displacement of the upper drill string is more pronounced than the longitudinal vibration displacement. The stabilization time of longitudinal vibration is about 150 s, whereas transverse vibration and torsional speed stabilize within approximately 100 s.</p> Conclusions <p>The results provide a useful reference for optimizing oscillation drag reduction tools and guiding their field application.</p>