The mid-infrared (MIR) spectral region, which corresponds to molecular vibrational and rotational energy level transitions, contains a wealth of molecular energy level information. By employing techniques such as Cavity Ring-Down Spectroscopy (CRDS), precise measurements of MIR spectra can be conducted, enabling the validation of fundamental physical laws, the inversion of fundamental physical constants, and the detection of trace gases. However, technical noise from temperature fluctuations, mechanical vibrations, and current noise causes free-running quantum cascade laser (QCL) to suffer from high-frequency noise, typically broadening the linewidth to the MHz range, thus reducing spectral resolution. Moreover, long-term drift in the laser frequency due to temperature and current fluctuations hinders high-precision spectroscopy, particularly for narrow-linewidth nonlinear spectroscopy, such as saturated absorption and multiphoton absorption spectroscopy.This paper presents a method that combines optical feedback with an optical phase-locked loop (OPLL) for offset frequency locking, aimed at generating a mid-infrared (MIR) laser with superior frequency characteristics. Strong optical feedback is employed to narrow the linewidth of the quantum cascade laser (QCL) acting as slave laser, thereby alleviating the challenges associated with phase locking. The OPLL is leverage to frequency-offset lock the slave laser to an ultra-narrow laser. By adjusting the offset frequency, fine control of the slave laser is achieved. To ensure tight phase locking, the OPLL is based on the ADF4007, incorporating a phase lead circuit to compensate for phase lag, effectively broadening the system's loop bandwidth.In this paper, initially, the fundamental principles of the optical phase-locked loop were theoretically analyzed, and a basic model was established. The influence of loop bandwidth on locking performance was also investigated. Upon achieving phase locking using the combined optical feedback and OPLL system, the magnitude of the beatnote of the two lasers was improved by 66 dBm, with phase noise suppressed to -81 dBc/Hz@2kHz in the low-frequency region and -101 dBc/Hz@2MHz in the high-frequency region.The frequency noise power spectral density of both the master and slave lasers was obtained via the error signal in the closed-loop system. Significant suppression of frequency noise was observed for the slave laser across both low- and high-frequency regions, with suppression ratios reaching 86 dB at 100 Hz and 55 dB at 400 kHz. The frequency noise of the slave laser in the low-frequency domain was found to be comparable to that of the master laser. Based on the white noise response region in the frequency noise spectrum (from 200 Hz to 400 kHz), the locked slave laser linewidth was determined to be approximately 3 Hz, narrowing the initial MHz-level linewidth to match the Hz-level linewidth of the master laser. Finally, the locked laser is used to conduct cavity ringdown spectroscopy, achieving an improvement factor of 5 in the signal-to-noise ratio of the ringdown signal.In future work, this frequency-stabilized laser will be applied to high-precision spectroscopy for the detection of radiocarbon isotopes.