A device for detecting light intensity, a display screen and a mobile terminal are provided. The device for detecting light intensity includes a controller, and a first photosensitive sensor and a second photosensitive sensor which are electrically coupled to the controller, the first photosensitive sensor and the second photosensitive sensor being spaced apart and located in a same illumination environment, and the controller is configured to, when an external beam illuminates the first photosensitive sensor, perform calculation based on a difference value between illumination parameters of the first photosensitive sensor and the second photosensitive sensor to obtain a light intensity of the external beam.