A fluid separating device comprises: a cylinder; a plurality of separators disposed around a cylinder; a first elastic piece disposed between one of the separators and the cylinder and applying an elastic force to the separator outwardly in the radial direction of the cylinder; a first guiding device passing through the cylinder axially and configured to reciprocate between an expanded position and a contracted position in the axial direction of the cylinder; a second guiding device penetrating the cylinder, connected to the separator at one end, and slidably fitted with the first guiding device at the other end via a fitting surface. The fluid separating device eliminates the friction between the separator and the inner wall of the wellhole when descending, therefore descending to the bottom of the well quickly.