The invention is suitable for the technical field of semiconductor transistor preparation, and provides a preparation method for a flexible transistor, which comprises the following steps of: transferring an obtained hexagonal boron nitride h-BN thin film to the surface of a preset substrate, manufacturing a conductive channel, source and drain electrodes, a gate dielectric layer and a gate electrode on the h-BN thin film to obtain a transistor sample, spin-coating a flexible substrate solution on the transistor sample and carrying out drying treatment to obtain a flexible film formed on the transistor sample, and stripping the transistor sample and the flexible film from the preset substrate to obtain the flexible transistor. According to the preparation method for the flexible transistor, the problems of alignment deviation and performance degradation when the transistor is directly prepared on the flexible substrate are avoided, and meanwhile, the flexible film is adopted to coat the transistor sample, so that the problem that the electrode of the flexible transistor is easy to fall off in the bending process is solved.