Fthe Tiantong mobile satellite communication, we propose a turbo equalization to remove ISI. However, the Log-MAP algorithm is sensitive to SNR estimation. Aiming at this problem, we propose a method of SNR estimation based on Chirp signal in FCCH of Tiantong system to ensure the performance of turbo equalizer. The simulation results show:SNR estimation error range of 0.2 dB can be ensured and BER can reach 10^-3 under condition of 3 dB Eb/N0.