The Si(ll1) surface structures induced by deposition of Au atoms were investigated by RHEED system. When Au atoms were deposited on the Si(ll1) $7 imes7$ surfade, the dependence of structures and phases on the substrate temperatures and coverages was drastic. For O.1ML to 0.4ML of coverage the $7 imes7$ structure changes to $7 imes7$ + $5 imes2$ structure as temperature increases to $350^{circ}C$-$750^{circ}C$. Between 0.4M1 to 1.OML the phase changed to $5 imes 2,alpha- sqrt{3} imes sqrt{3},eta- sqrt{3} imes sqrt{3}$ structure according to the substrate temperature and coverages. When the coverages exceeds O.SML, the 6 x 6 structure appears at the substrate temperature range between $270^{circ}C$-$370^{circ}C$ and compeletely transforms to 6 x6 at 1,OML. The isothermal desorption of Au on Si(ll1) surface investigated by using AES in the $alpha- sqrt{3} imes sqrt{3},5 imes 2$ structures shows that the desorption energys of $alpha- sqrt{3} imes sqrt{3}$ and 5 x 2 were 79Kcal/mol and 82 Kcal/mol respectively.