Abstract: To reduce the interference effects of the flow field between the upwind and downwind rotor, the double-rotor wind turbine drivetrain is featured a long span and many support points, causing complex load characteristics of the double-rotor wind turbine drivetrain supported by a long-span and flexible mainframe. In the work, a dynamic model of a type of double-rotor wind turbine drivetrain is established considering the mainframe’s flexibility. The structural strength of gears and the mainframe is analyzed. The results show that the contact strength and bending strength of gears as well as the structural strength of the mainframe satisfy the design requirement. The supporting deformation of the mainframe is beneficial to comply with the relative deformations between components.Reducing the mainframe’s flexibility appropriately is beneficial to reduce the axial misalignments between upwind and downwind main shaft bearings when the drivetrain is loaded.