Abstract: How to reduce the micro-defects of supersmooth optical surface is one of the research hotspots of manufacturing technology of ultra-precision optical element. A kind of novel precision optical fabrication method called non-adiabatic near-field optical induced smoothing surface microstructure was introduced to remove the surface scratches and digs after conventional polishing process. After establishing the geometry models of microstructures on supersmooth surfaces of silicon, the electric field excited by microstructure under the irradiation of 532 nm laser was numerical simulated by finite difference time domain (FDTD). From the comparison of the maximum intensity of the electric field excited by the microstructure with different sizes, it can be seen that the maximum of local electric field intensity approximately increase linearly with the scale of the microstructure increase. It also shows an increasing trend with gradient of microstructure increase while the peak value is less than 25.5 nm. The physics map of the smoothing of microstructure on silicon surface is described by the numerical simulation of electric field modulated by microstructure under laser irradiation, which gives a way to explain the non-adiabatic near-field optical etching process.