Provided are a method for transferring a compound semiconductor single crystal thin film layer and a method for preparing a single crystal GaAs—OI composite wafer, including: preparing a graphite transition layer on a first substrate; growing the compound semiconductor single crystal thin film layer on the graphite transition layer; preparing a first dielectric layer on the compound semiconductor single crystal thin film layer; preparing a second dielectric layer on a second substrate; combining the first substrate and the second substrate by bonding the first dielectric layer and the second dielectric layer; applying a lateral external pressure, such that the compound semiconductor single crystal thin film layer and the first substrate are transversely split at the graphite transition layer, and the compound semiconductor single crystal thin film layer is transferred to the second substrate.