The present invention discloses a GaN HEMT transistor with impact energy release capability for use in aerospace irradiation environment and preparation method thereof. The transistor includes a substrate layer, a gallium nitride layer, a barrier layer, and a gate structure successively arranged from bottom to top. The gallium nitride layers on both sides of the barrier layer are respectively provided with a source electrode and a drain electrode on the top surface. The gate structure is located near the source electrode and includes a p-type gallium nitride layer, a dielectric layer, an Ohmic metal pillar, and a Schottky metal layer. The present invention solves the breakdown problem caused by the inability to release impact energy during the switching process by introducing an asymmetric multi-integrated gate structure.