The invention provides a double-propeller power device which comprises a first propeller, a second propeller, a forward and reverse rotation driving part and a mounting seat; the first propeller and the second propeller are rotatably arranged on the mounting seat. The forward and reverse rotation driving part is a cam mechanism and comprises a forward rotation driving part, a reverse rotation driving part and a sliding piece. The forward rotation driving part and the reverse rotation driving part are rotatably mounted on the mounting seat respectively. The diameter of the forward rotation driving part is larger than that of the reverse rotation driving part, and the reverse rotation driving part is arranged on the side of the forward rotation driving part. The first propeller and the forward rotation driving part are relatively fixed, and the second propeller and the reverse rotation driving part are relatively fixed. And the forward rotation driving part is movably connected with thereverse rotation driving part through the sliding piece. And the sliding piece is slidably arranged on the mounting seat along the axial direction of a rotating shaft. The forward rotation driving part rotating forwards drives the reverse rotation driving part to rotate reversely through the sliding piece. The structural strength is high; high efficiency and energy conservation are realized.