Nitrogen (N) as well as water is the most limiting resources for plant growth in drylands. However, it is unknown how soil N transformation is limited by rainfall amount and which step is the rate-limiting step of N transformation in drylands. For mechanistically and comprehensively understanding soil N transformation process, it’s very useful to focus on soil microbial communities associated with each step of N transformation. Here, we briefly divided N transformation process into three steps, i.e. organic matter degradation step, mineralization step and nitrification step, which are primarily driven by fungi, prokaryote and ammonia-oxidizers, respectively. Microbial response to drought is various depending on the taxa, so we expected each step show different change along a rainfall gradient. We collected soil samples from three black locust forests along a rainfall gradient and analyzed extractable N and microbial communities. As a result, fungal, prokaryotic and ammonia-oxidizers community composition all dramatically changed along the rainfall gradient, as strong decomposers and nitrifiers increased. Accordingly, dissolved organic N, ammonium N and nitrate N content increased along the rainfall gradient. Thus, the rainfall gradient did not create a specific rate-limiting step, but almost equally affected every step of N transformation by controlling important microbial groups.