An optical feedback cavity ring-down technique (OF-CRD), in which the retro-reflection of the ring-down cavity (RDC) is re-injected into the oscillator cavity of a Fabry-Perot diode laser and causes the spectral fluctuation of the diode laser, is developed for ultra-high reflectivity measurement of optical mirrors. Due to the optical feedback-induced spectral fluctuation, the spectral line of the diode laser is occasionally in resonance with one or more RDC modes, resulting in an enhancement of the coupling efficiency of the laser power into the RDC and the occurrence of resonance peaks in the amplitude of the CRD output signal. These resonance peaks are employed in a CRD experimental setup for high reflectivity measurement of optical mirrors at 1064 nm. In the CRD setup, a pair of cavity mirrors, with reflectivities higher than 99.99%, is used. The reflectivity of both cavity mirrors is determined to be 99.99606% with an uncertainty of only 0.00003%. With a folded cavity configuration, the reflectivities of three mirrors with incident angles of 0, 22.5, and 45 degrees, are measured, and the results are 99.9459±0.0004%, 99.9755±0.0005%, and 99.9621±0.0006%, respectively.