Optical resonators with controllable Q factors are key components in many areas of optical physics and engineering. We propose and investigate a Q-factor controllable system composed of two directly coupled microring resonators, one of which is tunable and coupled to dual waveguides. By shifting the resonance of the controllable microring, the Q factor of the system as well as the other microring changes significantly. We have demonstrated wide-range controllable Q factors based on this structure in silicon-on-insulator, for example. The influences of spectral detuning and coupling strength between two resonators on the variation of Q factors are studied in detail experimentally. Then, we explore its applications in optical buffering. Tunable fast-to-slow/slow-to-fast light has been carried out by switching the system between the high-Q state and low-Q state. Moreover, optical pulse capture and release are also achievable using this structure with dynamic tuning, and the photon storage properties are investigated. The proposed Q-factor tunable system is simple, flexible, and realizable in various integrated photonic platforms, allowing for potential applications in on-chip optical communications and quantum information processing.