Abstract: In order to study the diurnal variation of N₂O and CO₂ from paddy field, and determine the best time for observation, a field experiment was conducted with static-chamber and gas chromatograph. The results showed that, nitrogen fertilizer had a significant role in promoting the emissions of N₂O and CO₂. The diurnal variation of the emission of N₂O had obvious difference in each treatment, but the flux of CO₂ had little difference in each treatment. During the whole observation period (120 h), the emission of N₂O from the check treatment, not only changes little, but also very lower. The emission of N₂O changes little before and after fertilization in 24 h, but increase significantly in 48-96 h, and decreased in 96-120 h. The diurnal variation of the emission of CO₂ in paddy soil were similar in each treatments, there weren’t significant difference in the paddy soil before fertilization. The emission of CO₂ of different observation period of 24-48 h, 48-72 h and 72-96 h had a trends of decreased first and then decreased in each treatment, and the flux of CO₂ of nitrogen treatment were significantly higher than that in check treatment. Based on the correct analysis, the average flux of CO₂ and N₂O were more close to the emission of observation of 9:00-11:00, and could represent the emission of the day and finally determine the gas samples collection time was 9:00-11:00.