Abstract: Through the analysis of requirements of ADS on the target, LBE (lead bismuth eutectic) was selected as the ADS target materials. With different radii and heights of the target, the energy spectrum, the number in different locations and the total number of neutron leakage were calculated by MCNPX. As SSR and SSW cards connected the MCNPX and MCNP, the history of a proton started from the target reaction was simulated. The concept of proton efficiency was put forward. When the total power and k_eff keep constant, increasing the proton efficiency will solve one of the difficult aspects of ADS. Combining the specific conditions of the target’s location and variation of the target’s radius in the reactor core, statistics data were obtained by MCNP. The conclusions are drawn to maximize the efficiency of the proton, and then combined with ADS’s characteristics, the design optimization program of the target was proposed.