In recent years,no-tillage (NT) technology is widely adopted in the rice-growing area of Southern China. However,it was not clear whether the technology could mitigate the greenhouse effect in rice paddy. The effects of different tillage methods on annual methane (CH_4) and nitrous oxide (N_2O) emissions,soil carbon sequestration,net global warming potential (GWP) and greenhouse gas intensity (GHGI) were studied by field experiments in double rice-cropping systems in 20132014. Methane and N_2O fluxes were measured using static chamber method,and the soil carbon sequestration was estimated by the changes in topsoil (0~ 20 cm) organic carbon (SOC) density. The treatments included NT,rotary tillage (RT) and conventional tillage (CT) in this paper. The results showed that annual CH_4 emissions ranged from 233.5 kg·hm~(-2) for the CT plots to 404.4 kg·hm~(-2) for the NT plots,53.7%~ 66.5% of which derived from the late-rice season. Annual N_2O emission was 4.00 ~ 4.82 kg(N)·hm~(-2)·a~(-1) in the double ricecropping systems. Topsoil SOC sequestration rate was estimated to be 0.36 t(C)·hm~(-2)·a~(-1) for the RT plots and 1.31 t(C)·hm~(-2)·a~(-1) for the NT plots. Annual grain yield was 15.2~ 17.1 t·hm~(-2) for the double cropping rice. Compared with the CT,NT slightly enhanced the net annual GWP,while it was remarkably enhanced by RT. The GHGI significantly increased for the RT and NT plots as compared to the CT plots. The results of this preliminary study suggested that RT and NT could increase comprehensive greenhouse effect under the short-term experiment in Chinese double rice-cropping systems. However,further studies are needed find out the long-term effect of NT on carbon sequestration and mitigation.