For the Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation (OFDM/OQAM) system has no cyclic prefix, it is sensitive to time error and has a high requirement for frequency offset estimation in fast time-varying ground-air channel with large Doppler frequency offset, an AutoCorrelation Estimation (ACE) time frequency synchronization algorithm for OFDM/OQAM system in ground-air channel was proposed. In the algorithm, the symbol timing was used to achieve fast acquisition and timing with fewer auxiliary sequences. The frequency offset estimation was carried out by optimizing the autocorrelation sequence and performing two autocorrelation operations. The final frequency offset was obtained by weighting and averaging the estimated frequency offset of the two operations. The simulation results showed that symbol timing correlation peak of the ACE increased 3 compared with the Modified Linear Square (MLS) and Training Sequence 2 (TR2) algorithm. There was a 10dB SNR (Signal-to-Noise Ratio) gain when BER (Bit Error Rate) was 10 ^-2 at the en-route state of ground-air channel, and there was a 3dB SNR gain when the system BER was 10 ^-3 at the arrival state of ground-air channel. The simulation results show that the ACE algorithm further enhances time frequency synchronization accuracy and bit error performance.