Abstract: The invention discloses an LCD with an ambient light sense function and its method. The method compraises the step of: coupling a capacitor to a source electrode of a thin film transistor; calculating a transmission time which required by a potential change from the reduction of electric charges; and finally, calculating an intensity of the ambient light according to the transmission time. The invention further discloses an ambient light sense circuit having a thin film transistor, a capacitor and a read-out switch. As the ambient light changes, a leakage current of the thin film transistor is changed accordingly, and the transmission time which required by the potential change is therefore changed. The read-out switch transmits said potential to a data read-out line in order to calculate the intensity of the ambient light from the transmission time. The LCD of this invention includes a plurality of capacitors, a plurality of read-out switches and a processing module.