Si nano-crystal films were prepared by pulsed laser ablation in extra direct current electric field that vertical to plume axis in Ar gas of 10 Pa at room temperature.Substrates were fixed on the arc bracket with the ablation spot as the circular center. The morphology and composition of films were characterized by scanning electron microscopy graphs, Raman scattering spectra and x-ray diffraction spectra. It drew that the average size of grains increasing with the addition of voltage, and the size of grains near negative board bigger than those near positive board. The area density of grains decrease at first and then increase and decrease finally, furthermore, the distribution character changed from negative board to positive board.