Turbo code and LDPC code are traditionally employed in the channel coding, which is used for the communication between Unmanned Aerial Vehicles (UAVs) and ground receiving equipment. Unfortunately, the disadvantage of both turbo code and LDPC code is high complexity of decoding, high time-consumption, and high-priced hardware cost. Moreover, LDPC code may lead to error floor at high Signal-to-Noise Ratio (SNR). Oppositely, it is more efficient for decoding using Gray code in UAVs. The reason is that it has lower computational complexity and shorter operation time. Furthermore, for hardware development, it is able to achieve simple and low-power architecture. Thus, in this study, a UAV image transmission decoding algorithm is proposed based on adaptive hard/soft decoding of Gray code. In this algorithm, the parity bit decoding mechanism is designed for switching between hard- and soft-decoding. The simulation results indicate that the algorithm is efficient and reliable. It is also proved that the proposed algorithm can be adaptive to different requirements of image precision through adaptively selecting the suitable decoding method, which also speeds up the procedure of decoding significantly.