The present disclosure discloses a display device and a display method thereof. The display device includes: a display screen is configured to be switched between a landscape state and a portrait state; an information collection unit is configured to collect an image of a viewer; a sight concentration area determination unit is configured to determine a sight concentration area of the viewer before the display screen is switched between the landscape state and the portrait state; a to-be-displayed picture determination unit is configured to determine a to-be-displayed picture after the display screen is switched between the landscape state and the portrait state; and a central processing unit is configured to process the to-be-displayed picture, wherein the processed to-be-display picture may cover a whole display surface after the display screen is switched between the landscape state and the portrait state.