Abstract: The design of offshore riser has the direct effect on drilling safety, cycle and cost, so one of the key issues for the drilling of offshore exploration wells is how to design a proper riser to increase the drilling speed and reduce the drilling cost while ensuring the drilling safety. The strength and stability of small-size riser was analyzed based on boundary constraint conditions, combined with seasonal effect of hydrometeorology in the sea area of the operation. Then it was applied on site. It is proved that as for the operation in the Beibuwan sea area in non-Typhoon seasons, the small-size riser technology can solve the long design time and high cost of the conventional Ø508 mm riser and cover the shortage of "blind replacement" cementing of Ø508 mm× Ø339.73 mm riser assembly. Its successful application breaks the limitation of conventional Ø508 mm riser on wellhead stability requirement, provides the new reference for the future design of risers in exploration wells in the Beibuwan Basin, and establishes the foundation for sustainable safe and efficient operation of exploration wells in the Beibuwan Basin in the future.