The invention relates to a safe early warning beam structure for a longitudinal-beam-free middle bearing type arch bridge and an early warning method of the structure. A structure of the longitudinal-beam-free middle bearing type arch bridge does not adopt a longitudinal main beam, and when a hanging rod of the arch bridge fractures, beam falling accidents can be caused. The safe early warning beam structure comprises a continuous longitudinal beam consisting of a middle spanning connecting beam, a middle spanning support beam, a side spanning connecting beam and a side spanning support beam, wherein the continuous longitudinal beam extends to a cross beam between ribs, the middle spanning support beam forms a bag hanger on the hanging rod cross beam through the cross beam support beam and the connecting hanging rod, the top surface of the middle spanning connecting beam is provided with a longitudinal semitransparent communicating pipe, the inside of the middle spanning connecting beam is filled with low-volatility lubricating oil, the liquid level height differences of lubricating oil at the two ends of the communicating pipe are observed by the semitransparent communicating pipe, and the monitoring on the deformation of the middle spanning connecting beam is realized. The structure and the method have the advantages that the longitudinal beam basically bears no load in the operation stage, when small probability events such as hanging rod fracture occur, the longitudinal beam starts to take effects, the occurrence of the beam falling accidents is prevented, through the adopted communicating pipe, the deformation condition of the longitudinal beam can be observed, and the feasibility of monitoring the hanging rod safety on the basis of longitudinal beam deformation is improved.