The bioinspired structure of the mushroom-shaped micropillar has been considered a blueprint of functionalized adhesives due to its prominent dry adhesive performance. Among the design strategies, the geometrical parameters of the stalk and tip are of significance for improving their adhesion performance. In this study, mushroom-shaped micropillars in different diameters of the stalk and tip are fabricated by a new fabrication approach, and the adhesion measurements are performed to study the influences of loading conditions and geometrical parameters on the pull-off force. The experimental and numerical results suggest that the stalk and tip diameters strongly affect the interfacial detachment behavior and the pull-off force. Two detachment modes are distinguished by the positions of the crack initiation. Finite elemental analyses reveal the detachment mechanisms by the interfacial stress distribution and damage evolution. According to the detachment mechanisms, a structure design strategy for mushroom-shaped micropillar with maximum pull-off force is proposed. The present studies provide a fresh insight into the adhesion behaviors of mushroom-shaped micropillars and contribute to the future adhesive design.