With the aim of forecasting the wheat-aphid relationships under different precipitation in the future atmospheric CO2 environment, the effects of different atmospheric CO2 concentration on Rhopalsiphum padi population under different soil water levels in Open-Top chambers were studied. The results showed that Rhopalsiphum padi population grew constantly with the continuous rising of atmospheric CO2 and it grew more quickly when CO2 concentration increased from 350 microliters.L-1 to 550 microliters.L-1. In each CO2 concentration treatment, R. padi population were distinct under different soil water level, and they were the highest under 60% of field water capacity treatment. When CO2 concentration increased from 350 microliters.L-1 to 550 microliters.L-1, the increase of R. padi population under 60% of field water capacity treatment was higher than that under 40% and 80% treatment. When CO2 concentration increased from 550 microliters.L-1 to 700 microliters.L-1, the increases of R. padi population under 60% and 40% soil water treatments were the same and both higher than that under 80% treatment. These results suggested that R. padi population would grow more quickly from the beginning to the middle of the 21st century and bring more damages to the wheat in arid and semiarid area.