YuLan-OneSim is a novel social simulator that simulates human social behavior using agents based on a large-scale language model (LLM). Compared to existing research, it allows for the creation and modification of scenarios through natural language interaction without code, and provides 50 basic scenarios across eight fields, including economics, sociology, and politics. The LLM can be fine-tuned through external feedback to improve simulation quality, and it boasts scalability to handle up to 100,000 agents. Furthermore, it provides an AI social researcher function that automates the process of setting up a simulation environment, analyzing results, and generating and reviewing technical reports simply by presenting a research topic.