The invention discloses an inner supporting device used for supporting a foundation pit. The inner supporting device comprises a supporting body, a first connecting disc, a second connecting disc, connecting batten plates and constraining pull rods. The supporting body comprises two hollow pipes which are arranged in parallel. The first connecting disc is connected to one end of the supporting body and is connected with the two hollow pipes at the same time. The second connecting disc is connected to the other end of the supporting body and is also connected with the two hollow pipes at the same time. The two ends of the connecting batten plates are arranged on the outer walls of the two hollow pipes correspondingly. The constraining pull rods penetrate the hollow pipes, and the two ends of the constraining pull rods are arranged on the pipe walls of the hollow pipes. By means of the inner supporting device used for supporting the foundation pit, the two hollow pipes are arranged in parallel, the first connecting disc, the second connecting disc and the connecting batten plates are matched for mutually fixing the two hollow pipes, afterwards, concrete is poured into the hollow pipes, and then supporting bodies are connected for supporting a crown beam or circuit purlin. Rigidity is high, the mass is small, mounting and demounting are convenient, the construction efficiency is improved, and repeated utilization can be achieved.