At present, the uncertainty of the mechanical parameters of the isolated rubber bearing is seldom considered and offshore bridge with or without the isolated device is also seldom studied based on failure probability. The uncertainty of the mechanical parameters for the rubber bearing according to test data from different manufactures was researched. Then, a non-linear dynamic analysis model of the offshore bridge was established. After the randomness of the bridge structure, the isolator and the earthquake ground motion were considered, 90 bridge-isolator-earthquake ground motion samples were generated by using the Latin-Hyper-Square sampling method. By Sap2000 non-linear dynamic time history analysis program, the seismic response of every sample was calculated. A large amount of response data were analyzed by using regression analysis method, and the seismic vulnerability curves of the bridge pier and the bearing corresponding different damage states were obtained. Then the comparative analysis of vulnerability for offshore bridges with or without the isolated device was carried out. The result appears that under the same damage state and earthquake, the failure probability of the non-isolated bridge pier is larger than the isolated bridge pier, the damage of the non-isolated pot bearing is larger than the isolated rubber bearing, and the bearing is more likely damaged than the bridge pier. After using the isolation technology, the probabilities of serious damage state or nearly collapsed state of the bridge pier are very low, so the repairable probability of the bridge pier after earthquake is very large. On the contrary, the probability of serious damage state for the non-isolated bridge is the largest, which means that the repairable probability of the bridge pier after earthquake is very low, some irreparable damage may have already occurred.