Soil microorganisms are important components of soil ecosystem and play central roles in biogeochemical cycling such as organic matter decomposition, mineral nutrient release, and energy transformation. Along with the intensive comprehension of the importance of biodiversity and the rapid development of methodology, more and more studies have focused on soil microbial diversity. This review introduces the current development of methodology and affecting factors of soil microbial diversity. We also discussed the directions of future research on soil microbial diversity.