Self-Interference has been significantly reduced by current cancelation methods for the practical design of Full- Duplex wireless. However, the residual self-interference is still much stronger than the thermal noise due to many factors, e.g. phase noise in local oscillator, I/Q imbalance, thermal noise and so on, limiting the self-interference cancelation. In this paper, the influence of the thermal noise on the active self-interference cancelation (ASIC) for wideband Full-Duplex OFDM wireless system is analytically studied and demonstrated. We propose a little modification to the structure of data packet of IEEE 802.11g to reduce the impact of the thermal noise on the active selfinterference cancelation (ASIC) for Full-Duplex OFDM wireless. The ADS-Matlab co-simulation results show that we can reduce the residual self-interference to only 1.5dB higher than the receiver thermal noise.