Abstract:As an aseismatic measure of highway bridges, collapse-proof system is the method for seismic design and retrofitting, which consist of adequate seat length, seismic restrainers and unseating prevention devices. Unseating prevention devices are the ultimate security installment to prevent the girders form falling off the piers when bridge hit by earthquake, the effect of them are influenced by the design parameters. Based on the relational design standards at home and abroad, the seismic response of structures with different cable-unseating prevention devices, the pressure of unseating prevention devices and the effect of collapse-proof changed with cable length and design moving value were compared. The result show that the effect of collapse-proof decrease as the cable length and design moving value increase,the pressure of unseating prevention devices is larger than the design bearing capacity while the prarmeters are both smaller.