Abstract: In order to research the effect of multiple wet-dry cycles and soil aggregate size on soil respiration especially Birch effect, based on three different aggregate size surface soil (0-20 cm) for the tested soil, through the use of indoor incubation test method, research the multiple wet-dry cycles and different soil aggregate size to Birch effect. The results showed that, after water promoted the soil respiration, increased the soil microbial biomass, but the surge effect did not last long. Respiratory rate was peak after rewet 3h, and the more wet-dry cycles, the lower respiration rate. Different soil aggregate grain size of Birch effect of strength different, but they had not a simple linear relationship. The results also showed that, the soil aggregates could protect soil organic matter from decomposing by microbe, while multiple wet-dry cycles interfere with this protection function and improved the organic carbon biocompatibility. A large amount of carbon source from Birch Effects came from the new organic matter of exposure, a little the accumulation of solutes in cells during dry period. It was worth noting that before the new organic matter from the exposure was mineralized and decomposed, other process might still exist.