Abstract: A greenhouse incubation test was conducted to study the effects of amendment with different amounts of maize and rice straws on the soil pH, CO₂, and exchangeable NH₄⁺ under continuous flooded condition. The results showed that in a near-neutral soil, straw amendment could decrease soil pH, with a significant difference (P＜0.05) between the treatments of 4 g straws·kg^-1 and control (CK), but no significant difference (P＞0.05) between the treatments of 1 g straws·kg^-1and CK. The CO₂ content in soil solution increased with increasing rate of straw amendment, with the peak value being 35.9% and 31.9% (v/v) in the treatments of 1 g maize straw·kg^-1and 1 g rice straw·kg^-1, respectively. These two treatments had significantly higher CO₂ contents (P＜0.05) than CK, but no obvious difference between themselves (P＞0.05). In treatments 4 g maize straw·kg^-1 and 4 g rice straw·kg^-1, the peak value of CO₂ content was 54.2% and 41.8% (v/v), respectively, being significantly higher than that of CK (P＜0.01), and significantly different between themselves (P＜0.05). Under nonN fertilization, soil NH₄⁺N concentration decreased after straw amendment, and the increase of the amendment rate caused a further decrease of soil NH₄⁺N concentration, with a significant difference (P＜0.05) between the doses of 1 and 4 g straw·kg^-1. Under N fertilization, soil NH₄⁺N concentration increased after 1 g straw·kg^-1amendment, but decreased after amendment with 4 g straw·kg^-1. No significant differences were observed between maize straw and rice straw amendment regardless with or without N fertilization (P＞0.05).