Recently, the first batch of two gearboxes independently developed and manufactured by DHHI for 8.34MW double-fed on-shore wind turbines were full load and overload tested successfully. It is verified by disassembling for two times that, the cleanliness reaches a higher class of 14/10, and gear dressing and meshing as well as the processing quality of the components are approved by the customer, the certification authority and the supervisor.