Abstract: In order to meet the need of precise compensation of chromatic dispersion in optical fiber link with long distance and high bit rate, channel dispersion measurement technique based on second order lowest power of radio frequency (RF) signal was studied and demonstrated. The chromatic dispersion in optical fiber link was measured by the phase difference between RF signals that loaded to two sidebands of spectrum. By loading RF signal on the transmitter, the periodic relationship between the power of RF signal in the receiver and optical fiber dispersion was obtained. The position of second lowest RF signal power was gotten by simulation of relationship curve between the power of RF signal in the receiver and optical fiber dispersion. The results show that, the dispersion measuring error in this system is in the range of ±10ps/nm. Comparing with the technique based on first order lowest power of RF signal, dispersion measuring technique based on second order lowest power of RF signal can satisfy the need of measuring large fiber dispersion for high chromatic dispersion value.