【Objective】 Jianghan Plain is one of the most important wheat producing areas in Hubei Province, and high relative air moisture is a major limitation on wheat grain yield. Under the conditions of global climate change, relative air moisture increased as well as air temperature. This research was carried out to study the effect of increasing relative air moisture on wheat grain yield, in order to provide a theoretical basis for promoting wheat production in Jianghan Plain. 【Method】The research was carried out based on the analysis of air moisture characteristics in Jianghan Plain from 1983-2013. During the experiment, air moisture was increased to 100% by artificial chamber for 10 days at booting stage of wheat, and the normal air moisture treatment was used as CK, samples were taken at 5 d, 10 d after high air moisture control, and 5 d, 15 d after recovery from all treatments. The effects of high air moisture on photosynthetic characteristics, SPAD value in flag leaf and top 3rd leaf, course of leaf senescence, root activity, plant height, and accumulation of dry matter, grain yield and yield components were studied. 【Result】Air moisture from 1983 to 2013 in Jianghan Plain fluctuated with a 2-5-year circle, and the average air moisture was over 80% during booting stage in most of the years. The air moisture at booting stage in Jianghan Plain in 2011-2012 and 2012-2013 was high, and averaged 77.4% and 79.1%, respectively. Increasing air moisture at booting stage decreased SPAD value in flag leaf and top 3~(rd) leaf, and the difference was not significant at 5 d later, but significant at 10 d later. When air moisture returned to normal, there was a difference in leaf SPAD value between high air moisture treatment and CK, but still inferior to CK. The effects of high air moisture on photosynthetic rate in flag leaf was in agreement with SPAD value. High air moisture reduced photosynthetic rate in flag leaf and removing high air moisture treatment, the difference between high air moisture treatment and CK reduced. Increased air moisture to 100%, MDA content in flag leaf and top 3rd leaf increased, suggesting that high air moisture quickened senescence in leaf. Further analysis showed that root activity reduced as well. Removing high air moisture treatment, the difference of MDA in leaf and root activity between CK and high air moisture treatment reduced, but was still significant, which mean the effects of high air moisture on the above index was not reversal. With the increasing of relative air moisture, the amount of dry matter and grain yield decreased. Compared with CK, at maturity, dry matter of high air moisture treatment decreased by 5%, and grain yield decreased 10.0%, respectively. For further analysis, the decrease of grain yield was attributed to spike weight and grain amount per spike, decreased by 6.0% and 4.2%, respectively, at maturity compared to CK. 【Conclusion】Under the conditions of this experiment, high air moisture at booting stage decreased SPAD value and photosynthetic rate in flag leaf, quickened membrane peroxidating, reduced root activity, and induced to the decrease of biomass and grain yield decreased as well.