The utility model provides a GaN-based vertical power transistor device. The GaN-based vertical power transistor device comprises an N-type GaN substrate, a P-type GaN substrate, a P-type GaN layer, aP-type GaN layer and a P-type GaN layer, wherein the N-type GaN epitaxial layer is formed on the N-type GaN substrate; the Al (In, Ga) N back barrier layer is formed on the N-type GaN epitaxial layer; a thin barrier Al (In, Ga) N/GaN heterostructure formed on the Al (In, Ga) N back barrier layer; wherein the passivation layer, the grid electrode and the source electrode are formed on the thin barrier Al (In, Ga) N/GaN heterostructure, and the drain electrode is formed on the N-type GaN substrate. According to the GaN-based vertical power transistor device disclosed by the utility model, the process difficulty of the GaN-based vertical power transistor is effectively reduced, so that the GaN-based vertical power transistor device is compatible with the process of a conventional GaN-based transverse device, and the application of the GaN-based vertical power transistor in higher current and power conversion is promoted.