The electron transport properties of a silicon atomic chain sandwiched between Au (100) leads are investigated by using the density functional theory combined with the non-equilibrium Green's function method.The breaking process of Au-Si4-Au nanoscale junctions is simulated.The conductance and the corresponding cohesion energy as a function of distance dz are obtained.With the increase of distance,the conductance decreases.When dz =18.098 (A),there is a minimum value of cohesion energy.The nanoscale structure of junctions is most stable,and the equilibrium conductance is 1.71G0 (G0 =2e2 /h) at this time.The Ⅰ-Ⅴ curves of junctions at equilibrium position show linear characteristics.