Abstract: With the increasing in life of platform service,the environmental conditions for platform service become disadvantage due to the change in sea conditions in Bohai Sea.It is proposed that in Bohai Sea,the environmental condition for offshore platform structure design should be 100 year return period rather than 50 year return period.Through comparison analysis on the 50 year/100 year return period environmental condition for structure design of partial center platform and wellhead platform in the Bohai Sea,it is proposed that 100 year return period should be used to replace 50 year return period in the offshore platform structure design in Bohai Sea.