Time-reversal (TR) wideband communication could harvest the energy from the rich-scattering environment and enjoy the unique spatial and temporal focusing effect. However, the performance degrades in the presence of carrier frequency offset (CFO), which introduces an additional phase linear in time. CFO estimators could mitigate its effect. Yet, conventional CFO estimators cannot work well regarding the tiny CFO due to the high sampling rate in wideband TR systems. To address this issue, we propose four CFO estimators which are capable to estimate very small CFO with very high accuracy. Theoretical performance analyses of the proposed estimators are derived. Realizing that phase wrapping could introduce a large bias into estimation, we also derive the condition for phase wrapping avoidance. Extensive experimental results in real environment demonstrate the superiority and applicability of the proposed methods.