The utility model discloses a supporting structure for the long edges of a strip-shaped and rectangular foundation pit. Two or more lenticular beam devices are arranged on each long edge part of the foundation pit, a diagonal bracing is arranged at the position between the two long edges and between every two adjacent lenticular beam devices for supporting the foundation pit together, the diagonal bracings generate pre-stress by adjusting a lifting jack, and the lenticular beam devices generate pre-stress by adjusting the tightness degree of steel strands. The supporting structure is small in occupied space on the whole, brings convenience to excavation of the foundation pit and improves the efficiency. Meanwhile, the components of the supporting structure are mostly sectional materials in standard sizes and are connected through bolt pieces, therefore, installation and disassembly are both very convenient, the reutilization ratio is high and the foundation pit supporting cost is reduced on the whole.