Data reconciliation protocol is one of the important steps in quantum key distribution(QKD), and its efficiency directly affects the key rate of QKD. Therefore, a continuous variable QKD data reconciliation protocol based on concatenated polar coding andmultistage decoding is proposed. Based on the multistage coded modulation system, the proposed protocol uses the concatenated Polar codes with better error correction performance as component codes in the multistage decoding. The performance of the protocol is analyzed by simulation. The simulation results show that the reconciliation efficiency of the proposed protocol is greatly improved, while the bit error rate of the key decreases greatly at the same time. When the signal-to-noise ratio is equal to 0.5 dB, the bit error rate of the protocol is less than 10-3. This protocol is of great value to the application of continuous-variable QKD.