The invention provides a field-effect transistor structure and a fabrication method thereof. The fabrication comprises the steps of providing a substrate, and depositing at least one layer of first material and at least one layer of second material on a surface of the substrate; defining an active region and a shallow groove isolation region; etching the active region to form a channel region, a source region and a drain region; corroding the first material layer or the second material layer in the channel region to obtain at least one nanowire channel; depositing a dielectric layer and a gridstructure layer on a surface of the nanowire channel; and fabricating a grid electrode, a source electrode and a drain electrode on surfaces of the grid structure layer, the active region and the drain region to complete fabrication of the field-effect transistor. By the scheme, the stacked Si or SiGe material layer forms the three-dimensional stacked annular grid nanowire channel, the cross section of the channel is expanded on the same planar region, the device performance is improved, the grid control capability is improved, the device stability is also improved, the carrier transmission capability is improved as well as the device size is reduced, the device performance is improved, the source-drain doping step is omitted, and the technology is simple in process.