In recent years, soil Cd Contamination has become more and more prominent, so BCs were widely applied to agricultural soils as a soil conditioner. The effects and mechanism of biochar on remediation of Cd contaminated soils, especially on the soil microbial activity and function were revealed in this paper. A pot experiment was conducted to mainly focuses on investigating how different BCs ratios application to different particle size soil aggregates influences microbial community structure and functional diversity, with the method of Biolog-Eco micro plate. Analysis results all showed that:the application of BCs had a positive effect on Cd contaminated soil microbial community, which improved microbial carbon metabolic activity and functional diversity, in particular the 2.5% BCs treatment was the most significant. The soil microbial functional diversity showed "V" type distribution rule in soil aggregates, which the 5~1mm and <0.25mm aggregates were highest.With the increased of Cd pollution and the protection of BC in <0.25mm aggregates. The McIntosh index of soil microbial communities rised by 32.68%~135.52%,and the uniformity of microbial species greatly changed. The utilization ability of carbon source were studied and indicated that microbes preference for other types in Cd contaminated soil. The further analysis demonstrated that there was a significant difference in soil microbial metabolic activities between the BCs treatment and the Cd control group, especially carboxylic acids and carbohydrates carbon source utilization.