A micro-controller embedded online simulation debugging system, including a communication port control module, a state control module, a debugging command control module, and a hardware breakpoint monitoring and triggering module. The above-mentioned modules are controlled inside the chip through the special debugging command set sent by the host The entire online simulation debugging system works; it can complete the complex boundary scan of the chip through the standard test boundary scan, control the microcontroller chip from the normal mode to the debugging mode according to the external command, and through the debugging communication interface with the host, the program can be from Download or read from any location in the memory of the microcontroller, support single-step debugging of the target system, support software and hardware breakpoints, view or modify the contents of special function registers, data memory and program memory inside the chip in real time, monitor address bus and data bus , to achieve real-time logic tracking and other functions. The structure is clear and simple, the operation effect is efficient, and the real-time monitoring is accurate.