Stratospheric ozone depletion occurs mainly over polar regions during the spring when the solar Ultraviolet B-band (280-315 nm, UV-B) radiation is most intense in a year， but over the Qing Tibetan Plateau region, the highest intensity is from June to September when the amount of UV-B radiation reaching the regions is more than that in the adjacent areas lying in the same latitude by 10%. From June to September is just the time of plant’s germination, development, and reproduction in the alpine region. UV-B radiation may alter the reproduction of the forage plant, oat (Avena sativa.), which plays the vital role in developing indigenous herdsman’s animal husbandry industry. The responses of oat yield and its components to the enhanced ultraviolet B band irradiation under the field condition were surveyed. The effect shows that the grain yield is decreased significantly by strengthened UV-B irradiation, and at the same time the main consequence is the decrease in both the number of ears per square meter and the number of grains per ear, but the weight of 1 000 grains appears not significantly different. Compared with the same respective location in a spikelet, the grain weight is decreased significantly under the treated condition, mostly because of the decreases in the number of the third and forth floret grain and the grain weight at those respective positions, and the percentage of the first and second floret grain and their weight are evidently approved on the contrary.