A tunneling field effect transistor with a new structure and a preparation method thereof are provided. The tunneling field effect transistor includes an active region between a source and a drain, a gate dielectric layer, and a gate located on a side of the gate dielectric layer deviating from the source, and a tunneling region disposed between the gate dielectric layer and the source and in contact with both the gate dielectric layer and the source. The source includes at least a first area and a second area perpendicularly connected in an “L” shape. The tunneling region is in contact with at least the first area and the second area. The gate dielectric layer is in contact with at least the tunneling region and the source.