An adaptive and precise chromatic dispersion (CD) estimation algorithm with a large dispersion monitoring range is proposed based on a two-stage structure for long haul coherent optical communication systems. A coarse estimation of chromatic dispersion is obtained by employing the auto correlation of signal power waveform (ACSPW). Afterwards, a precise CD value can be estimated by using the modified constant modulus (CMA) scheme. Simulation results show that the measured error value is less than 35 ps/nm by using the proposed algorithm, and the accuracy is improved about four-times compared to the conventional ACSPW algorithm. When the reference error rate is 10-2, the power penalty compared to the ACSPW algorithm is improved by 8 dB.