The invention discloses a GaN vertical heterojunction field-effect transistor with a composite low-K current barrier layer, mainly including a barrier layer, a channel layer, an n<+>-GaN substrate and a drain electrode from top to bottom. An upper part of the barrier layer is provided with a source electrode and a grid electrode. A current barrier layer and an n-GaN buffer layer are arranged between the channel layer and the n<+>-GaN substrate. The center of the current barrier layer is provided with an aperture with the width of LAP. The aperture is embedded in an upper part of the n<+>-GaN substrate. The current barrier layer is made of an insulation dielectric medium and is internally provided with a low-K insulation dielectric layer. The current barrier layer is internally provided with the low-K insulation dielectric layer, so that the breakdown voltage of the device of the invention reaches the withstand voltage limit of a GaN material. In addition, the structure of the device of the invention has no difficulty in p-type doping, the barrier effect of the insulation dielectric medium to current exceeds that of p-GaN to current, and the leakage current of the drain electrode in a cut-off state is lowered.