Global climate change, including climate deterioration and extreme weather events, has serious impacts on reliability of bridge superstructure. Global warming and increasing velocity of wind associate with the increase of CO2 level play a dominate role in reliability degradation. For the highway bridge in offshore environment, a main factor of reinforcing steel corrosion is the invasion of chloride ion, which can cause durable damage of the structures. Moreover, temperature rises will increase corrosion rates. In addition, changes in maximum wind speeds may increase expected wind loads on bridge structures. This paper develops a reliability analysis model to assess the reliability degradation of the highway bridge superstructure under (i) base case, (ii) temperature rising case, (iii) wind speed changing case, and (iv) combination of case (ii) and case (iii). The process is illustrated by studying the reliability of a offshore highway bridge using simplified models of the structure. It is demonstrated that the reliability degradation will be greatly accelerated taking account of climate change. The life expectancy of the structure will be 10 years and 70 years lower than base case if the target reliability is 4.5.