The present invention discloses a thin-film transistor structure with a three-dimensional fin-shape channel and a preparation method thereof. The preparation method includes following steps: (a) depositing and etching a bottom gate electrode on a substrate; (b) depositing a bottom dielectric layer at an upper part of a structure obtained from the step (a), and sequentially depositing a semiconductor film on the bottom dielectric layer; (c) etching the semiconductor film to obtain a fin-type channel; (d) respectively depositing an ohmic contact layer, a source electrode and a drain electrode on the semiconductor film located at both sides of the fin-shape channel, and etching; (e) depositing a top dielectric layer and a top gate electrode at an upper part of a structure obtained from the step (d); and (f) etching the top gate electrode, an completing a preparation of a thin-film transistor with a dual-gate three-dimensional fin-shape channel.