A three-dimension elastoplastic model had been developed to study the space effect of the soil-nailing excavation protection. The positive corner effect

negative corner effect and layered excavation were emphatically analyzed. The researches showed that: the negative corner of excavation could reduce the displacement of excavation and the force of soil-nail; and its influence was once more than the depth of the excavation; meanwhile

the displacement of the excavation and the force of soil-nailing were much larger in the positive corner; and its influence is near to 3 times of the depth of the excavation; the space effect of soil-nailing pit could be used plenarily by layered excavation; its influence was near to the depth of the excavation. It was proved that three-dimension numeric analysis of the soil-nail structure was very useable.