The invention discloses an optimized L-type tunneling field effect transistor and a preparation method thereof and mainly solves the problems of low on state current and severe bipolar effect of an existing device. The optimized L-type tunneling field effect transistor comprises an SOI (silicon on insulator) substrate (1), isolation grooves (2), a source region (3), a channel region (4), a drain region (6), a gate region (5) and a conducting layer (7), wherein the isolation grooves (2) are located on two sides of the SOI substrate (1), and the source region (3), the channel region (4) and thedrain region (6) are located on the upper surface of the SOI substrate; the gate region (5) is located on the upper side of the channel region (4); the source region (3) is made of a germanium semiconductor material, the gate region (5) is of a hetero-gate dielectric structure, a high-k dielectric material is adopted on one side close to the source region, and a low-k dielectric material is adopted on one side close to the drain region; a space S is formed between the drain region (6) and the right margin of the gate region (5). The optimized L-type tunneling field effect transistor can effectively inhibit the bipolar effect, increases drive current and can be applied to manufacture of large-scale integrated circuits.