A two-phase immersion-type heat dissipation structure having high density heat dissipation fins is provided. The two-phase immersion-type heat dissipation structure having high density heat dissipation fins includes a heat dissipation substrate, a plurality of sheet-like heat dissipation fins, and a reinforcement structure. A bottom surface of the heat dissipation substrate is in contact with a heating element immersed in a two-phase coolant. The plurality of sheet-like heat dissipation fins are integrally formed on an upper surface of the heat dissipation substrate and arranged in high density. An angle between at least one of the sheet-like heat dissipation fins and the upper surface of the heat dissipation substrate is from 60° to 120°. At least one of the sheet-like heat dissipation fins has a length from 50 mm to 120 mm, a width from 0.1 mm to 0.35 mm, and a height from 2 mm to 8 mm.