The invention is directed to a mask plate, an exposure system comprising a mask plate and an exposing method. The mask plate comprises a light transmitting region, a light shielding region, and a light reflecting region for reflecting exposure light to the light shielding region, with the pattern of the light from the transmitting region and reflecting region corresponding to the pattern of the region exposed to a first and a second substrate respectively. When exposure light irradiates on the mask plate, it passes through the light transmitting region and exposes the first substrate. The light reflecting region reflects the exposure light to a principal reflection structure which further reflects the light for exposing the second substrate. The first and second substrate may be exposed via the same mask plate to minimize waste of exposure light to save production time and efficiency.