In this paper, an improved adaptive coding and modulation scheme with hybrid switching standard is proposed for UAV-to-Ground free space optical (FSO) communication to mitigate the degradation of turbulence intensity variation. In order to improve bits efficiency in different turbulence, a channel estimator based on Gated Recurrent Unit (GRU) and a hybrid switching standard based on frame error rate (FER) of LDPC decoding are applied. Simulation results show that the GRU estimator achieves approximately 34.9% improvement in training time compared to the LSTM estimator, without degradation in system performance. Moreover, the hybrid switching standard significantly improves the signal-to-noise ratio (SNR) switching threshold deviation of the ACM scheme from 1.8 dB and 4 dB, which were observed in moderate turbulence conditions, to an average of 0.35 dB. This improvement allows for the effective implementation of the ACM scheme in different turbulence intensities at a relatively small cost, thereby enhancing the communication quality of FSO systems in atmospheric channels characterized by turbulent variations.