The invention relates to the field of construction, and discloses a semi-solid formed back ridge fixing device which comprises a supporting platform and a locking assembly. A back ridge is placed on the supporting platform and abuts against a template through the locking assembly. The supporting platform comprises two main ribs fixed perpendicular to the template, wherein the outer side of one main rib is provided with a first rack. The locking assembly comprises a pre-tightening member and a final tightening member. The pre-tightening member comprises two horizontal rods, and the outer side of one horizontal rod is provided with a second rack. The two horizontal rods are respectively matched with the two main ribs, and the second rack is matched with the first rack. The final tightening member includes two vertical rods respectively connected with the two horizontal rods of the pre-tightening member and an eccentric wheel connected between the two vertical rods. The fixing device effectively solves the problem that the traditional back ridge locking structure is complicated, simplifies the back rib fixing structure, and improves the back ridge assembly and disassembly efficiency.