A five-year field experiment was carried out in Suzhou, Jiangsu province to draw on the benefits of scientific evaluation of emissions of greenhouse gases (GHGs) and provide scientific instructions to develop rational measures for reducing GHGs emission from rice fields in the lower reaches of Yangtze River. By using static chamber/gas chromatographic techniques, this experiment was simultaneously measured for CH_4 and N_2O emissions under five rice-based cropping patterns: rice-fallow (T_1), rice-ryegrass (T_2), rice-Chinese milk vetch (T_3), rice-wheat (T_4), and rice-rape (T_5). The results showed that the total CH_4 and N_2O emissions and global warming potentials (GWPs) in rice growing season, non-rice growing season and whole annual cycle were significantly influenced by cropping patterns. Annual total CH_4 emissions under different cropping patterns were: T_3(294.97 kg/hm~2)> T_1(151.04 kg/hm~2)> T_5(123.89 kg/hm~2)> T_4(119.33 kg/hm~2)> T_2(111.92 kg/hm~2). Annual total N_2O emissions under different cropping patterns followed the order of T_5 (3.26 kg/hm~2) > T_4 (2.56 kg/hm~2) > T_2 (2.33 kg/hm~2) > T_3 (2.26 kg/hm~2) > T_1 (1.42 kg/hm~2). Annual GWPs of CH_4 and N_2O were significantly higher in T_3 (8 857 kg/hm~2) than those in T_1, T_5, T_4 and T_2. These results indicate that rice-ryegrass could increase CH_4 emissions and intensify the greenhose effects in rice fields in the lower reaches of Yangtze River.