The structural properties of Wn　clusters (n=3—27) has been studied by employing the first-principles calculations based on the density functional theory. The most stable structures of clusters (n=3—7) with global energy minimum and optimized structures of clusters (n=8—27) with local energy minimum are determined. Based on the jellium model, the electronic configuration 1s21p61d102s21f142p63s23p62d104s22f143d101g181h223f14 is proposed which can explain well the electronic magic numbers and the relative stabilities of W clusters. The binding energy, the first and second differences of binding energies and the HOMO-LUMO gaps versus the number of atoms in the cluster are also analyzed, showing that W clusters become metallic very quickly with the increase of cluster size. This may also imply a quick change of bonding characters in the W clusters.