The invention discloses a heterojunction power device and a manufacturing method thereof, and mainly solves the problems of current collapse phenomenon and low breakdown voltage of the existing gallium nitride-based device. The heterojunction power device comprises a substrate (1), a transition layer (2), a barrier layer (3), a source groove (7), a drain groove (8), a source electrode (9), a drain contact (10), floating island metal (11), drain island metal (12), a grid electrode (14) and a passivation layer (16), wherein a gate island (4), a floating island (5) and a drain island (6) are sequentially arranged on the barrier layer from left to right; the floating island (5) is composed of 2n-1 independent P-type semiconductor blocks, the drain island (6) is composed of m P-type semiconductor cuboid blocks, and a groove (13) is formed between every two cuboid blocks; and metal is deposited on the inner portion, the front side, the rear side and the right side of the groove to form Schottky contact (15). Current collapse can be restrained, breakdown voltage is improved, forward blocking and reverse blocking are good, and the heterojunction power device can be used for a basic device of a power electronic system.