The purpose of the study was mainly to explore the influence caused by the worn-down condition of medical sole of shoes and different speeds on the ankle pronation degree. In the study, each subject was assigned to wear four different pairs of shoes in order which were made up of four different midsole height (19mm. 15mm. 11mm. 7mm) running on a treadmill at a speed of 5.2, 6.9, and 8.9 m/h. High-speed camera was used to record twenty subjects from the rear running on a treadmill. The video tape was digitized by operating a set of PEAK PERFORMANCE ANALIZING SYSTEM, and regression analysis was utilized to explore the relationship of the three variables。After data treatment, the results were listed as followed: 1. As far as the relationship between running speed and the ankle pronation degree was concerned, pronation degree increased with the increase of running speed.. 2. As far as the relationship between LB.shoes and the ankle pronation degree was concerned, pronation degree increased with the increase of the worn-down condition of medical sole of shoes. 3. As far as the influence caused by both running speed and LB.shoes insimultaneously was concerned, pronation degree increased with the increase of the running speed and the worn-down condition of medical sole of shoes. 4. The regression formula, Y=6.13+1.028 × X1+0.428 × X2, was established to represent the relationship among the pronation degree of the ankle, running speed and worn-down condition of medical sole of shoes.