An automatic indoor lighting system and a realizing method relate to the field of daily life articles. The lighting system comprises a curtain body and a controller. Indoor lighting quantity can be automatically controlled according to indoor light intensity. The present invention has the benefits that a photosensitive sensor arranged in the controller can automatically sense indoor and outdoor light, and the indoor light is adjusted by regulating the opening width of a window gauze according to light intensity, so the special requirements of people for the curtain are met.