The invention provides a tunneling transistor with a horizontal quasi coaxial cable structure and a forming method thereof. The tunneling transistor comprises a semiconductor substrate, a channel region, a drain region or a source region and a gate structure, wherein the semiconductor substrate has a first doping type; the semiconductor substrate is a source region or a drain region; the channel region is formed on the semiconductor substrate; an insulating layer is formed in the region on the semiconductor substrate, in which the channel region is not formed; the drain region or the source region is formed on the channel region and the insulating layer and has a second doping type; a first part of the channel region is coated by a first part of the drain region or the source region; the gate structure is formed on the first part of the drain region or the source region; and the first part of the drain region or the source region is coated by the gate structure. According to the tunneling transistor provided by the embodiment of the invention, the driving capacity of a TFET (Tunneling Field Effect Transistor) device can be improved.