A long-term stability control scheme of the dynamic cavity length based on coupled optoelectronic oscillator is proposed. When the cavity length of the optical resonator changes, the resonant phase variation of two selected positions in the optical resonator is measured by the IQ mixer, and the optical delay line in the regeneration cavity is feedback-controlled to following compensation of the regeneration cavity length, and the controlled mode-locked output of the coupled optoelectronic oscillator with variable cavity length is realized, to convert the changing cavity length into the changing resonator frequency for measurement. After systematic experiments, the optoelectronic oscillator can output a variable locked microwave signal, and keep the side mode suppression ratio better than 47.26 dB, the power jitter less than 0.28 dB, and the lock phase error jitter within ±1.5° within 1 hour.