Mineralization of soil organic carbon is one of the important ways to greenhouse gas emissions (CO_2), reducing greenhouse gas emissions in the land use and increasing soil carbon converge ability is of great significance to slow down global warming. Biochar can improve soil physical and chemical properties, increase crop yield and regulate soil microbial ecology. This article adopted the way of outdoor pot experiment, elected kochia scoparia as grass plants, to study the improvement effects of reed, rice, smooth cordgrass straw and their biochar returning and its impact on soil respiration, carbon balance and its microbial mechanism. Results showed that straw and biochar could improve soil fertility and promote plant growth, and the improvement effect of biochar was slightly better. Soil respiration of straw biochar returning was significantly lower than that of straw returning directly, and reed straw biochar was the lowest. Straw returning directly could promote microbial activity indicators such as beta-glycosidase, dehydrogenase activity and soil microbial quantity, and enhance soil respiration as a consequence. But straw biochar returning had no significant role in promoting, but certain inhibition, which might be due to low content of straw biochar and its degradation-resistant.