The invention provides a fixing device and a method for fixing a side wing component of a vehicle rear seat to a vehicle body. The fixing device comprises an upper fixing component, a middle fixing component, a lower fixing component, an upper locking component, a middle locking component and a lower locking component, wherein the upper fixing component, the middle fixing component and the lower fixing component are arranged on a side wing body, the upper locking component, the middle locking component and the lower locking component are arranged on the vehicle body, the upper fixing component is matched with the upper locking component in a fastened and locked manner so that the side wing component is fixed along the longitudinal direction of a vehicle, the middle fixing component is matched with the middle locking component in a fastened and locked manner so that the side wing component is fixed along the transverse direction of the vehicle, and the lower fixing component is matched with the lower locking component in a fastened and locked manner so that the side wing component is fixed along the height direction and the longitudinal direction of the vehicle.