A water-activated power generating device, comprising a first module (100) having a first electrode plate (22) and a second electrode plate (31). The water-activated power generating device further comprises a first supporting structure (11), a second supporting structure (12) and two water storage layers (61, 62). The first electrode plate and the second electrode plate of the water-activated power generating device are fixed with a first fixing component (42), and a first insulating layer (51) is disposed between the first electrode plate and the second electrode plate. The water-activated power generating device further comprises a third electrode plate (21) and a fourth electrode plate (32), wherein the third electrode plate is fixed on the first supporting structure (11) with a second fixing component (41), and the fourth electrode plate (32) is fixed on the second supporting structure (12) with a third fixing component (43).