In an asteroid momentum deflection mission， the existence of ejecta effects induces an apparent “amplification” of the system momentum. Existing studies predominantly focus on scenarios where a spacecraft impacts an asteroid’s geometric center. However， through theoretical derivations， this paper demonstrates that when the velocity vector of the spacecraft is non-parallel to that of the asteroid， an impact offset from the geometric center can result in a significantly greater deflection distance compared with a geometric center impact. Numerical simulations are conducted for a potentially hazardous asteroid， i.e.， Apophis， to evaluate the kinetic impact deflection by comparing the deflection distances resulting from the impacts at a geometric center and a non-geometric center under an optimized dual-pulse transfer orbit. The results reveal an average deflection distance of 923.59 km with a standard deviation of 273.29 km for geometric center impacts， whereas the impacts on a specific non-geometric surface yield an average deflection distance of 1 328.57 km and a standard deviation of 48.61 km. This translates to a 43.85% increase in the deflection distance and approximately a 5.6-fold reduction in the standard deviation， substantiating the method’s effectiveness. Addressing the lack of asteroid attitude information， this study employs a Monte Carlo method to generate 100 000 random attitude samples for the simulation to manage uncertainties. The findings confirm the theoretical feasibility of this approach， and demonstrate its potential to significantly reduce the uncertainties in asteroid kinetic impact defense missions. Under invariant impact conditions， non-geometric center impacts amplify the deflection distance， underscoring a considerable research value.