To probe the mechanism of differences in CH4 and N2O emission among rice cultivars, this pot experiment was conduced to measure CH4 and N2O emission fluxes and plant characteristics of rice cultivars by static closed chamber method and gas chromatograph technique. The results showed that the maximum values of CH4 and N2O emission appeared at the heading stage and the booting stage respectively for the early rice. For the late rice, the maximum values of CH4 and N2O emission appeared at the shooting stage and the milky stage respectively. The differences of CH4 and N2O emission among different cultivars were significant. For the early rice, tiller number, root volume and root dry weight were significantly and positively related to CH4 emission fluxes, and root volume and root dry weight showed significant positive correlation with N2O emission fluxes. For the late rice, CH4 emission fluxes was positively correlated with root volume and root dry weight, and N2O emission fluxes was negatively correlated with tiller number, root volume and root dry weight. The GWPs of yield per unit area of the traditional early rice was 1.77 times as much as that of the hybrid rice, and for the late rice, there was only a small difference. Therefore, tiller number, root volume and root dry weight were the important factors influencing CH4 and N2O emission from the paddy field.