A guest-induced reversible crystal-structure transformation is identified in a new 3D covalent organic framework (COF) by comprehensive analyses using powder X-ray diffraction, organic vapor sorption isotherm, and Xe-129 NMR spectroscopy. The revolving imine bond in interpenetrating 3D networks is uncovered as the key to the dynamic behavior, the potential applications of which are illustrated by gas separation and heterogeneous catalysis, thus paving the way to the design of stimuli responsive and multifunctional COF materials.