Abstract: The common management of straw is burning in the field, which is considered as a convenient and economical method for farmers to deal with them in China. However, the burning of straw enhances the release of greenhouse gases including CO2. Turning crop residues into biochar under low temperature (usually<700℃) and limited oxygen conditions has been recently proven as a promising approach for the long term carbon sequestration. However, up to now, the quantity of carbon emission from crop straw burning and the potential of carbon sequestration by turning straw into biochar in China are still unavailable. Hence, in this paper, the quantity was estimated. Based on the data of crop yield from 2001 to 2010 in China, the major straw (rice, wheat, corn and soybean) output was calculated according to the ratio of grain to straw. The proportion and amount of burned straw were quantitatively analyzed. The total amounts of CO and CO2 emission were estimated according to the emission factors derived from references, and the total carbon emission was calculated based on the CO and CO2 emission without thinking of the other forms of C emission. Moreover, biochars were derived from major crop straw under lab conditions (a typical slow pyrolysis process, heated in a muffle furnace at a speed of approximately 20℃ min-1 under limited oxygen and held at 500℃ for 4 h) and the carbon sequestration amount of biochars were estimated according to the carbon contents and yields of biochars. The results showed that annually production of crop straw in China was about 5.1×108 t, and about 21.6% of them were burned, which led to high CO, CO2 and carbon emission, which were about 1.15×107、1.57×108 and 4.77×107 t, respectively. Meanwhile, the average carbon contents and yields of biochars were 63.2% and 30%, respectively. Although the stability of biochar and the effect of pyrolysis temperature on the carbon sequestration were not studied in this study, the annually carbon sequestration amount by turning straw into biochars was 0.96×108 t and about half of carbon emission was decreased annually if the amount of burned straw was turned into biochar, which indicated that turning straw into biochar was a promising approach for straw management.