We have studied the structure and melting transition of the Si(001) surface using the molecular dynamics simulation technique together with the Stillinger-Weber model potential. The structure of the simulated surface is of the dimerized (2×1) symmetry and the surface contains spontaneous defects. The dimers are symmetric and neither buckled nor twisted. The results are compared to scanning tunneling microscope (STM) experiments. The surface induced melting starts below the bulk melting point of the sample and is found to proceed by surface roughening along the direction of highest packing density.