Large-Scale Language Model (LLM)-based code generation agents are revolutionizing the software development paradigm. They possess three key characteristics: autonomy, expanded task scope, and enhanced engineering practicality. This paper systematically surveys the field of LLM-based code generation agents. It traces the technological evolution and systematically categorizes key technologies, including single-agent and multi-agent architectures. Furthermore, it presents agent applications across the entire SDLC, summarizes mainstream evaluation benchmarks and metrics, and lists representative tools. Finally, it analyzes key challenges and proposes long-term research directions for future research.