<p>Steam Assisted Gravity Drainage (SAGD) technology is crucial to the development of unconventional oil and gas resources. However, the complex operating conditions and dynamic challenges of high-displacement sucker-rod pumping systems limit economic efficiency and safety. This study investigated the dynamic characteristics of such systems in SAGD wells by incorporating the effects of well fluid flashing in the casing, tubing, and pump annulus. A new dynamic model is established to enhance system stability and efficiency. First, the study analyzed the flashing phenomenon qualitatively, demonstrating that it causes abrupt changes in wellbore pressure and temperature, which disrupt pump operation and reduce system stability. Then, the study constructed a comprehensive model that comprised a wellbore temperature field model, accounting for heat conduction, convection, and radiation; a liquid holdup model, based on mass and energy conservation, to determine gas–liquid proportions; a sucker-rod string dynamic model, reflecting elastic deformation and frictional effects; and a segmented tubing fluid column model, improving prediction accuracy through column partitioning. The model was validated against field data from an example well to verify the effectiveness of the proposed approach. The model predictions closely matched measured results, confirming accuracy and reliability. Accordingly, this paper proposes an optimization strategy that involves lowering the pump setting depth below the casing flashing point. This adjustment can reduce the adverse effects of flashing, thereby improving pump efficiency and operational stability. The results of this study provide a theoretical basis and technical guidance for optimizing the design and operation of high-displacement sucker-rod pumping systems in SAGD wells. They also extend understanding of flashing effects on well performance, offering both academic value and engineering applicability.</p>