The utility model relates to a double-disc straight blade impeller for a subsea mud lift pump, which is characterized by comprising a circular ring-shaped driving wheel. Both side faces of the driving wheel are symmetrically provided with a plurality of same radial straight blades in manner of a divergent shape; the center of a circular ring of the driving wheel is provided with a hub; the hub is evenly provided with four long blades at intervals; each long blade is respectively set into a whole with the corresponding radial straight blades on both side faces of the driving wheel; the four long blades at one side of the driving wheel are respectively provided with a connecting arm; the driving wheel is connected with a circular ring-shaped driven wheel through the four connecting arms; and both side faces of the driven wheel are symmetrically provided with a plurality of same radial straight blades in manner of the divergent shape. The double-disc straight blade impeller for the subsea mud lift pump has strong multiphase delivery capacity, jamming resistance, abrasion resistance, a flat flow head curve, a wide working range, a low axial force and no sealing pressure, therefore, the double-disc straight blade impeller can be widely used for the subsea mud lift pump in the marine riser-free drilling process.