【Objective】In recent years, tropospheric (ground level) ozone concentration was growing year by year because of the development of agriculture and industry, and had generated a degree of damage on crop production. 【Method】The effects of elevated ozone concentration (O3) on grain yield and its components and grain plumpness in five varieties of winter wheat (Tritcium aestivum L.) with a FACE (Free-Air Controlled Environment) system were studied in 2007-2009. The main-plot treatment had two levels of (O3): ambient level (A-O3) and 50% higher than ambient level (E-O3), and the sub-plot treatment had five typical varieties: Yannong 19, Yangmai 16, Jiaxin 002, Yangmai 15 and Yangfumai 2. The ozone treatment was imposed upon for the period from 5 March to 26 May in 2008 and from 6 March to 24 May in 2009, respectively. 【Result】 The O3 elevation decreased grain yield and its components (grain weight and numbers) significantly or very significantly. Under E-O3, the average grain yield was decreased by 19.74% (10.06%-34.53%) in two years, and 1000-grain-weight decreased by 17.88% (10.16%-29.47%), grain number per ear decreased by 3.47% (-1.53%-11.90%), but ear number increased by 0.95% (-14.58%-23.74% ) in different varieties, respectively. There was a significant or very significant difference among treatments, cultivars and years. The O3 elevation affected the development process of wheat grains, the grain length, width and thickness were decreased by 0%-4.16%, 7.95%-20.24% and 2.66%-11.00% under E-O3 condition, which led to the decrease of grain volume by 8.5%-31.5%. The O3 elevation affected grain filling process, the average grain filling rate decreased. Because of the changes of grain volume and grain weight, grain plumpness degree changed by -21.40%-3.76%, the grain shrinkage index increased by 0.23%-36.66%, respectively. 【Conclusion】 Under E-O3, grain yield decrease resulted mainly from the declining of grain weight which was caused by the decrease of grain filling rate and grain plumpness.