Fluorescence resonance energy transfer (FRET) serves as a versatile technique for quantifying intermolecular interactions by measuring the energy transfer between donor and acceptor molecules. In this work, a free-addressing FRET technique based on fluorescence lifetime measurements is proposed. Within the framework of a dual-color confocal microscopy, this method utilizes two galvanometric scanners to freely address a focused light to any locations on a sample and uses a time-correlated single photon counting board to capture the trigger signals from the scanners, and the arrival times of photons relative to previous laser pulses. Consequently, the fluorescence lifetime at any region of interest within the field-of-view can be obtained. Once the fluorescent lifetimes of donor fluorophores before and after bleaching the acceptor fluorophores are determined, the FRET efficiency at the targeted site can be further calculated. Compared with the traditional intensity-based FRET measurement method, this approach does not require special calibration operations and significantly reduces measurement times from minutes to milliseconds. We can envisage that the proposed technique can be widely applied to life science, medical diagnosis, materials science, and so on.