Abstract: Conservation tillage improves soil conditions, increases crop yield, and is also one of the key measures in lessening biodiversity loss of agricultural soils. A Field trial with split-plot design was conducted to investigate soil fauna and soil fertility under conservation tillage systems, the relation of which was discussed in this study. The results showed that straw returning significantly increased the amounts of agricultural soil fauna, especially for collembola and acari. The interaction between tillage type and straw returning amount was significant. Application of no-tillage added straw returning significantly improved soil organic matter content, but lowered soil pH value. Straw returning increased in soil available phosphorus content and soil total nitrogen and soil urinary activity, but decreased in catalase and invertase activity when compared to the initial condition of experiment. The dominant groups (collembola and acari) of soil fauna were highly correlated with soil organic matter content, and Coleoptera, Diplura and Chilopoda might be adapted to reside in relatively high pH value soils. In conclusion, conservation tillage can improve soil organic matter content and increase soil carbon pool which is beneficial to lessen greenhouse effect, and also increase the abundance of soil fauna. The abundance of soil fauna is well correlated to soil nutrients, which shows that soil fauna plays an important role in availability of soil nutrients utilized by plants in the agro-ecosystem.