The invention discloses a contra-rotating outer framework water-air dual-purpose engine. The engine mainly structurally comprises a supporting frame, an oil electric pipeline, a front thrust bearing, a peripheral bearing, a radome, an inner duct, an outer duct, a gas compressor, a ring-shaped combustion chamber, a worm wheel, a rear thrust bearing, a convergent tail spray tube, a central duct, an inner rotor, an outer rotor, a blade tongue-and-groove, a fan, an engine cover, a power transmission circuit, a conductive slide ring, an oil conveying pipeline, a convergent channel, a rotary joint, a metal fuel cavity, a metal-water reaction combustion chamber and a fan stator blade. The gas compressor and the worm wheel of the engine are not provided with a stator blade, and an outer frame rotor and an inner rotor are in counter rotating in an air working state, so that the gas compressor and the worm wheel can realize counter rotating, the absolute rotation speed of the rotor is lowered when the engine efficiency is improved, the axial dimension of the engine is shortened and the structure weight is reduced. When the engine works in water, the ring-shaped combustion chamber does not work, the inner and outer rotors are static, and power is produced by the metal-water reaction combustion chamber, so that water-spraying propulsion is realized.