The invention discloses a passive fluid driving device of an immersed cooling system. The passive fluid driving device comprises a heat conducting shell and a driving device, wherein the heat conducting shell is divided into an internal space and an external space, the internal space and the external space are used for storing a cooling liquid respectively, and at least one air outlet for making the external space communicate with the external space is formed in the heat conducting shell; the driving device comprises a pivot, a disturbing piece and an impeller, the pivot is provided with the heat conducting shell in a pivoting manner, the disturbing piece is fixed to the pivot inside the internal space, the impeller is positioned in the external space and is fixed to the pivot, the impeller is provided with a plurality of blades, a part of the blades correspond to the air outlet, the air outlet is used for discharging gas after evaporation of the cooling liquid, and a part of the blades are pushed by the gas to drive the impeller and the disturbing piece to rotate relative to the heat conducting shell.