An optical frequency comb phase-locked on an iodine frequency stabilized diode laser at 634 nm is constructed to transfer the accuracy and stability from the optical domain to the radio frequency domain. An external-cavity diode laser is frequency-stabilized on the Doppler-free absorption signals of the hyperfine transition R(80)8-4 using the third-harmonic detection technique. The instability of the ultra-stable optical oscillator is determined to be 7\times10^{-12} by a cesium atomic clock via the optical frequency comb’s mass frequency dividing technique.