Abstract: In order to study the effects of biodegradation agents in two kinds of straw returning (i.e. soil returning straw and mulching straw), changes of wheat straw components by biodegradation agents were studied under field in two kinds of straw returning, meanwhile effect of decomposed wheat straw on soil labile carbon was also conducted. Wheat straw was from field under wheat-maize rotation system. Three biodegradation agents (i.e. BW1, BW2, BW3) were selected from our own laboratory. Results indicated that, under soil returning straw patterns cellulose-straw degradation rate was BW2≈BW3 > BW1 in four weeks, and the rate was increased by 24.95%, 24.57%, 2.10% compared with CK1. In six weeks, hemicellulose-straw degradation rate was BW2 > BW3 > BW1, increased by 12.67%, 8.80%, 1.47% than CK1. In the mulching straw patterns, cellulose-straw degraded relatively slow, cellulose-straw degradation rate was BW2 > BW3 > BW1 in four weeks, increased by 26.52% , 24.01% , 21.02% than CK1. Hemicellulose-straw contents were changed obviously, hemicellulose-straw degradation rate of three biodegradation agents was BW2 > BW3 > BW1, increased by 22.90% , 20.00% , 9.32% compared with CK1. No obvious differences happened in three biodegradation agents to the lignin-straw degradation rate during two patterns. In the process of soil returning straw, the content of soil labile carbon was increased by 54.09% in biodegradation agent BW2 which was the highest. However, during mulching straw pattern, the content of soil labile carbon was increased by 34.58% in biodegradation agent BW3. Both the biodegradation agents BW2 and BW3 could degrade wheat straw high effectively in two patterns. It was found that microorganism agents by the soil returning straw patterns had better degradation effect, and the content of soil labile carbon was obviously increased.