A shaping knife for solid fuel comprises a pressing plate, a knife bar, set screws, lock nuts, a rotating rod, a handle, blades and a knife rest, wherein the pressing plate is located at the upper end of a combustor shell of a solid engine, the lower end of the knife bar penetrates through a center hole of the pressing plate, and is located in the combustor shell, the blades are located in the combustor shell, and are installed at the end of the knife bar through the knife rest, a graduated scale is fixed to the surface of the upper end of the knife bar, the geometric center of a knife bar installing hole is located at the position, of two thirds of the length, of the knife rest, the knife rest is made to be located on one side of the center line of the interior of the combustor shell, and therefore when the combustor shell is shaped, the blades which are installed at the two ends of the knife rest have different shaping areas. According to the shaping knife for the solid fuel, a mechanical shaping device is used for replacing an ordinary steel shaping tool which is used at present, propellant at the shaping position is cut, the quality of the propellant is ensured through a shaping size control method, the weighing frequency of the propellant is reduced, the shaping efficiency is improved, labor intensity is reduced, and the potential safety hazards are eliminated.