The disclosure provides a wind turbine generator and a control method thereof. The wind turbine generator comprises at least two power transmission systems connected each other in parallel and a control system comprising an upper controller and control subsystems corresponding to the power transmission systems and comprising bottom controllers. The bottom controllers monitor operating state parameters of functional units in corresponding power transmission systems, and when determining corresponding functional units meet abnormal conditions according to operating state parameters, send operating state parameters of corresponding functional units to the upper controller; the upper controller generates operating instructions when determining faults of the corresponding functional units occur according to operating state parameters of corresponding functional units, to control power transmission systems to work according to operation instructions. The wind turbine generator is fully used, and the energy production thereof is further increased.