Mode hopping causes varying degrees of degradation in the coherence of single-wavelength fiber ring lasers, which seriously affects the performance of optical systems. In this work, a method for coherence collapse suppression based on a matched interferometer is designed, and the suppression mechanism is analyzed. A space-light matched interferometer (SLMI) with adjustable arm difference and an all-fiber matched interferometer (AFMI) are constructed separately, and the suppression effect is verified experimentally. Experimental results show that when the equivalent arm difference of the SLMI continuously approaches the theoretical value, multi-mode-matching interference can be monitored. This is equivalent to single-longitudinal-mode laser interference, thereby successfully suppressing coherence collapse. The AFMI is compact and easy to incorporate into a fiber coherence detection system. It is found that the AFMI can effectively suppress the coherent collapse and the sharp increase of phase noise spectrum level introduced by random mode hopping; this helps to reduce the false alarm probability of the system. As a passive method, matched interferometers play a significant role in suppressing or evading coherence collapse caused by mode instability.