Method and device for adjusting projection display screen size of projector

The invention discloses a method and a device for adjusting a projection display screen size of a projector. In the method and the device for adjusting the projection display screen provided by the invention, the present environmental light brightness of the present service environment are obtained in real time; and then the size of the present projection display screen is adjusted in real time according to the correspondence of the obtained present environmental light brightness and the predetermined environmental light brightness to the size of the projection display screen. The method and the device for adjusting the projection display screen provided in the invention are capable of changing the projection display screen size according to the intensity of the environmental light.