Abstract: The present invention discloses a multistage variable burning rate solid rocket motor and a forming method. A multi-material composite fiber skeleton structure is embedded inside a propellant in the present invention, so that the original burning rate of the propellant presents multistage changes to achieve the function of multistage thrust. The fiber skeleton structure embedded in the solid rocket motor is formed by additive manufacturing, fixed in a combustion chamber, and then charged at one time to complete the forming of a motor grain. The design can greatly increase the burning rates of the propellants of end-burning and bore-burning motors, and can also conduct multistage adjustment for the burning rates of the motors by changing the fiber skeleton and structure, so as to satisfy the requirements of missile weapon systems for multistage power propulsion. The present invention greatly simplifies the technological production process of the existing single-chamber multi-thrust motor.