To simulate the plasmon-induced water splitting reaction with Au particle at the nanometer scale with mixed TDDFT/FDTD method, we firstly calculate the time-dependent spatial inhomogeneous scattering field generated by the truncated Au tetrahedron via FDTD++ package, then describe the time evolution trajectory dynamics of Au 20 @H 2 O system under the intensive near field by TDDFT/Ehrenfest scheme. With this treatmen- t, the hot electron injection is assumed to always appear around the interface between the metal cluster and the adsorbate, and the different sized NP provides the near field with different intensity to which Au 20 @H 2 O is subjected, as Figure shows.