1. A panoramic image sensor, used in a panoramic viewing system and including: a plurality of photo sensing units, arranged in said image sensor, and said photo sensing units being respectively formed with different photo sensing areas according to arranged locations, wherein said photo sensing areas of said photo sensing units being determined by an elliptical conical curved surface of a panoramic reflection mirror, central photo sensing areas of said photo sensing areas with lower illuminance are formed with a larger photo sensing area, and outer photo sensing areas of said photo sensing areas with higher illuminance are formed with a smaller photo sensing area; the different photo sensing areas of the photo sensing unit are designed to match gradients of the curved surface of the panoramic reflection mirror, different gradients of the curved surface of the panoramic reflection mirror map onto the different photo sensing areas of the photo sensing unit, the different photo sensing areas of the photo sensing unit have smaller area sizes corresponding to larger gradients of the elliptical conical curved surface of the panoramic reflection mirror and the different photo sensing areas of the photo sensing unit have larger area sizes corresponding to smaller gradients of the elliptical conical curved surface of the panoramic reflection mirror.