Unseating prevention devices(UPD) are used to prevent relative great displacement between supper-structure and sub-structure, and to protect the super-structure falling down from piers as the support loss capacity. Unseating prevention devices are the ultimate security installment in the collapse-proof system when the highway bridges encounter rare earthquake or unexpected earthquake. Based on the relational design standards at home and abroad, the paper is emphasis on the time-history analysis for structure with cable-unseating prevention devices under rare earthquake. The analysis results obtained show that the collapse-proof effectiveness of unseating prevention devices and the variation law of collapse-proof changing with cable length and design displacement value. What’s more, under rare seismic, the rational unseating prevention devices can ensure the ultimate security of the structure, increase the integrity and anti-pushing rigidity of the structure, and make the seismic load to be well-distributed among the piers. As a result, the unseating prevention devices can effectively avoid girder falling in strong seismic, achieving no collapsing in strong seismic.