The results from a laboratory experiment showed that the composition and total amount of CO₂, CH₄ and N₂O emitted from a clayey soil were affected significantly by water regime and amendment of wheat straw. Under the flooded conditions, the emission was small for N₂O, but large for CH₄,and CO₂; in contrast, under the aerobic conditions, the emission was not detectable for CH₄,but large for N₂O; the drainage of flooded water acceleseted N₂O emission, but depressed CH₄ emission. And the emissions of CO₂, CH₄ and N₂O under the flooded/drained alternate conditions were the middles between those under flooded conditions and under aerobic conditions. The overall potential for greenhouse effect (OPGE) caused by the emitted greenhouse gases, calculated according to their potential in absorbing thermal radiation, was the highest under the flooded conditions and the lowest under the flooded/drained alternate conditions. It clearly demonstrated that the change in water regime would not only alter the composition of greenhouse gases emitted from soil but OPGE as well.