Optical packet replication with accurate cycle and consistent pulse power is realized by using the semiconductor optical amplifier (SOA) optical fiber ring cavity. In order to suppress the amplitied spontaneous emission (ASE) noise and avoid the ring cavity resonance, the method of introducing non-circulation assistant light is proposed. Using the simplified model, the theoretical analysis and the simulation for the output noise and the signal-to-noise ratio (SNR) are carried out. The relation between output SNR and the duplication times is obtained. The impact of assistant light and attenuation coefficient upon SNR is analyzed in detail. The experiment results are consistent with theoretical results. In order to make the output pulse power of optical packet replication consistent, a SOA is used for the power equilibrium of the output packet. 15 times duplication with the SNR declining less than 3 dB and the pulse power keeping nearly consistent is implemented.