本文结合开发项目“基于C8051F040 单片机的嵌入式系统开发”，在深入研究嵌入式系统技术的基础上，提出了小型PLC 设计的系统方案。硬件结构以高性能的8 位嵌入式处理器C8051F040 为核心，充分利用其丰富的片上资源，扩展系统的输入输出功能。软件以开发的PLC 内核为核心，开发系统所需要的应用，将嵌入式PLC内核扩展为完整、实用的PLC 系统。-In this paper, the development project　C8051F040 MCU-based embedded system development　in-depth study of embedded system technology, based on a small PLC systems designed programs. Hardware structures to eight high-performance embedded processor C8051F040 as the core, take full advantage of its rich on-chip resources, the expansion of the system input and output functions. Software to develop the kernel at the core of the PLC to develop systems for applications, will be expanded core embedded PLC integrity, practical PLC system.