By using Stillinger-Weber potential, we have carried out the constant temperature molecular dynamics simulations of surface structures on Si(001) at different temperatures. Our results show that the dimers rearranged into p(2×1) cell are the primary structure on Si(001) surface. Besides this, trimers and c(2×2) metastable structures as well as two-dangling-bond single atoms are observed on the surface at different temperatures. Up to the surface melting temperature, these metastable structures disappear and the simple p(2×1) structure remains on the surface.