Objective: To investigate how interference from motor and cognitive tasks affects the postural stability of older adults while descending stairs. Methods: The study involved 52 older adults (mean age: 66.8 ± 3.6 years). Using the Vicon infrared motion capture system and Kistler force plate, kinematic and dynamic data were collected simultaneously during stair descent under three conditions: single-task, motor task, and cognitive task. Dynamic stability during stair descent was assessed using the Measure of Stability algorithm. Repeated measures ANOVA was applied to compare differences across conditions. Results: 1) Gait Parameters: Compared to the single-task condition, both step speed (P < 0.001) and step frequency (P < 0.001) were significantly reduced under motor and cognitive task conditions.tep length (P = 0.037) was also significantly reduced under the cognitive task condition compared to the single-task condition. 2) Anterior-Posterior Dynamic Stability: Compared to the single-task condition, centroid velocity (P < 0.001) and extrapolated centroid position (P < 0.001) were significantly increased, while dynamic stability (P < 0.001) was significantly decreased under both motor and cognitive task conditions. In comparison to the cognitive task condition, centroid displacement (P = 0.011) and velocity (P = 0.014) , as well as extrapolated centroid position (P < 0.001) , were significantly greater under the motor task condition. 3) Medial-Lateral Dynamic Stability: Compared to the single-task condition, centroid displacement (P < 0.001) was significantly reduced under both motor and cognitive task conditions. Additionally, the extrapolated centroid position (P = 0.001) was significantly reduced, and dynamic stability (P = 0.038) was significantly increased under the motor task condition compared to the single-task condition. Conclusion: The study found that older adults adjust their gait in response to dual-task interference while descending stairs by "slowing down step speed, reducing step frequency, and shortening step length." This adjustment helps maintain medial-lateral dynamic stability but significantly decreases anterior-posterior dynamic stability, thereby increasing the risk of falls.