Disclosed in the present application are a method and device for determining the position of a viewer and adjusting a viewing area, and a device for displaying three-dimensional video signals, such that the position of a viewer in front of an electronic device can be accurately determined and the viewing area can be adjusted according to the specific position, enabling the viewer to be unaware of any sudden viewing change when watching 3D signals. The method for determining the position of the viewer is applied in an electronic device comprising a display screen capable of displaying three-dimensional video signals. The viewing areas of the electronic device include a three-dimensional display area and a non-three-dimensional display area. The method comprises: acquiring the image in front of the electronic device; judging whether the image contains the face image of the viewer; if the image contains the face image, identifying at least one feature in the face image to determine the position of the viewer; according to the at least one feature, determining whether the viewing area of the viewer is a three-dimensional display area or a non-three-dimensional display area.