High efficiency postprocessing of continuous-variable quantum key distribution (CV-QKD) system has a significant impact on the secret key rate and transmission distance of the system. For a quantum channel with unknown prior characteristics, we have to sacrifice part (typically half) of the raw keys to estimate the channel parameters, which is used to assist in error correction and estimate the secret key rate. This introduces a trade-off between the secret key rate and the accuracy of parameter estimation when considering the finite-size effect. In this paper, we propose a high efficiency postprocessing method which uses all the raw keys for both parameter estimation and key extraction. The correcting party uses the extra data (used for phase compensation and synchronization etc.) to roughly estimate the quantum channel parameters, or she can use the results of the last block, then she selects a suitable code to correct the errors between them, finally she recovers the raw keys of the other side by a reverse mapping function after the success of error correction. Then, she uses all the raw keys of both sides for parameter estimation. We show that this method improves the accuracy of parameter estimation and the secret key rate of CV-QKD system.