Recently, the gearbox for 4.2MW wind turbine developed and manufactured by DHHI for export to a South Korean customer was DNV-GL certified and load tested for the prototype. Data from the test run and open package inspection showed that the results had advantage over the requirements of the latest IEC61400, and favorable comments from the international authoritative certification agency DNV-GL and the end user were obtained, making DHHI pass DNV-GL type testing successfully. This is another successful development of gearbox for low-wind-speed turbine for both onshore and offshore purposes after those for 5MW and 6MW wind turbines, symbolizing DHHI’s comprehensive levels for design, manufacture, test, etc. of wind turbine gearbox have ascended to international leading position, thus establishing a solid foundation for DHHI to further expand the domestic and overseas markets.