The flow rate of the extra-cylinder of the variable-cycle engine will change greatly with the transition of the working mode， and the corresponding internal/external contour blending flow brings challenges to the fuel injection scheme of the afterburner. In order to solve this problem， this paper numerically simulates the fuel distribution characteristics of afterburner in variable cycle engine under different modes， explores the influence of wide-range airflow change on fuel distribution， and forms a fuel injection optimization strategy for multi-modal afterburner. The results show that the velocity component of the afterburner mixture along the radial direction and the flow vortex induced by the lobe mixer are the key factors affecting the radial/circumferential diffusion of the fuel， respectively. In the small bypass ratio mode， the connotation-dominated high-temperature and high-speed flow makes the fuel diffusion velocity relatively consistent in a wide range. However， the radial velocity and vortex distribution of the gas change significantly in the large bypass ratio mode， resulting in obvious differences in the fuel diffusion velocity in different regions， which affects the uniformity of fuel distribution. On this basis， an optimization strategy is proposed to moderately increase the fuel flow rate of the nozzle at the middle position， and the results show that the uniformity of fuel distribution will be increased by up to 33.04%.