Prefabricated internal support system and construction method for foundation pit support system

The invention discloses a prefabricated internal support system and a construction method for a foundation pit support system. The prefabricated internal support system comprises a top beam (1), an enclosing purline and an inner support (2), wherein the inner support (2) is a truss type inner support (2) assembled by splicing a pre-stressed hollow square pile (3) and a node connecting piece; first end plates on the two ends of the truss type inner support (2) are in screwed connection with a connecting plate on the top beam (1), and the rest of the first end plates are in screwed connection with second end plates of the node connecting piece; the construction method comprises the key points that the pre-stressed hollow square pile (3) and the node connecting piece are assembled into the truss type inner support (2) in a splicing manner, and the two ends of the truss type inner support (2) are connected with the top beam (1). The prefabricated internal support system and the construction method for the foundation pit support system has the advantages that the system and the method are convenient and efficient, the construction speed is high, the construction period is short, the follow-up earth cutting and earth discharging are convenient, the dismounting process is also convenient, efficient and labor-saving, no safety potential hazard is caused, the system can be recycled, and the material is saved.