Abstract: Understanding the impact of elevated ozone (O₃) on crop yield is helpful for evaluating the yield loss and economic loss induced from atmospheric O_3pollution. Open Top Chamber (OTC) systems, established in Beijing and Dongguan, Guangdong Province, were implemented to study the impact of different concentrations of O_3on the winter wheat and rice, respectively. The crops were fumigated with O_3during their whole growth period. The exposure indices were calculated, and the response relationship between the exposed quantity of O_3and the yield of rice or winter wheat were obtained. The results showed that the critical level (based on AOT40, AOT40is the hourly meanozone concentration accumulated over a threshold ozone concentration of 40nL/L) of the rice were 4.95μL/(L·h) in Dongguan and 2.44μL/(L·h) for winter wheat for Beijing. Critical levels for crop in China were calculated based on the relationship between the exposed quantity of O_3and the yield of crops in previous studies. The critical levels were 4.950-9.506μL/(L·h) and 2.280-3.858μL/(L·h) for the rice and winter wheat in China, respectively. The sensitivity of rice to the atmospheric O_3increased from the North to the South of China, while that of winter wheat not significantly changed between different regions. Under the current environmental φ(O₃) condition, the relative yield loss was 2.70% (AOT40=2.68μL/(L·h)) for the rice in Dongguan and 12.85% (AOT40=6.72μL/(L·h)) for the winter wheat in Beijing. There are various crop growing environments and numerous crop categories in China, thus more studies should be conducted to establish O_3local exposed quantity-yield response relationships and further to reasonably assess the loss of regional crop yield.