Abstract: Based on the data of the observation system of surface layer in Dali National Climatic Observatory at the rice growing stage from 2008 to 2010.The diurnal and monthly variation of CO2 density and CO2 flux over the rice field were analyzed by eddycorrelation method,CH4 flux was contrasted with CO2 flux.The results showed that CO2 density presents obvious diurnal variation,CO2 density in the nighttime is much higher than that in the daytime,the vale usually appears at 14:00—18:00,the peak usually appears at sunrise.CO2 flux presents obvious diurnal and monthly variation.The vale usually appears at 14:00,the average lowest carbon dioxide flux is -1.068mg·m-2·s-1 in the diurnal variation.CO2 flux is negative from transplant to ripe over the rice field,the lowest carbon dioxide flux appears at jointing and heading stage,that means rice field economy system absorb CO2 from transplant to ripe.CO2 flux absorption is much strong than CH4 flux discharge.The rice field acts as a sink of CO2 for the whole growth stages.