The enhancement of light transmission through sub-wavelength slit is studied with our newly developed two dimensional simulation code of finite-difference time-domain method. The simulations verify the enhanced transmission that far exceeds the diffraction limit; the dynamics are helpful to understand in-depth the resultant beaming of light. Instead of one beam with a specific angle for a given wavelength [3-6], one additional beam with a different angle excited by the induced surface charge can be seen for the same wavelength from the electric field of different polarized direction. In additional to the interference of the scattered light with the transmitted light, the spatial de-coherence and coherence between the magnetic and electric fields is shown to be important for the transmitting process and the beaming mechanisms of the light. Thus, the dynamics will be illuminated in detail for deep understanding. The effect of different width of the exit groove on the enhanced transmission is also studied and explained as an application of above findings.