Aiming at the shortcoming that the M-th power based traditional phase recovery method cannot be used for high-order QAM signal constellations, a carrier phase recovery method for 16-QAM constellations is presented. The proposed method is able to applied in CO-OFDM system to implement blind phase recovery with low computational cost. In the verification experiment, the method is used in 112 Gb/s 1 040 km CO-OFDM transmission, and its performance is compared to those using the fourth-power estimator. Experimental results indicate that the proposed method significantly outperform the fourth-power estimator.