Abstract：Based on the analysis of the stratum¢s location and composition in Fuzhou city，it is found that stratum structure is important and can be divided into two types. In order to get a further acquaintanceship about the pit¢s working behavior in soft clay，a planar strain finite element programme is employed for numerical analysis. Mohr-Coulomb model is used to simulate the soil¢s stress and strain relation. A series of calculations via FEM are executed for the displacement response of foundation pits when the type of stratum structure，length or obliquity of soil nailing are changed. Compared with the pit¢s parietal movement under different conditions，some significant conclusions are obtained that the prepositive pile is the most important affecting factor for composite soil nailing. The cement mixed pile should be chosen for the prepositive pile of double stratum，and timber pile for three stratum. Because of the clay¢s weaker properties and wider sliding route than those of the others，the length of the soil nailing should be added to two times of the pit¢s depth which is different from that of those located in favorable soil. Finally，two cases are optimized based on above analysis，indicating a good identicalness between the results of calculation and measurement.
