RT-Thread is a real-time operating system (RTOS) for the Internet of Things.It provides basic functional elements such as thread scheduling,clock management,memory management,thread communication,interrupt management and so on.It has features of complete and rich components,high scalability,easy development,ultra-low power consumption,high security and so on.On the basis of in-depth analysis of functional elements and function call relationship of RT-Thread,the startup process of STM32 microcontroller chip is briefly given,focusing on the analysis of RT-Thread chip power-on,board-level initialization,timer initialization,scheduler initialization,thread creation,thread switch and other processes.It provides a technical basis for the transplantation of RT-Thread on different microcontrollers,and can also be used as a technical reference to analyze the startup process of other RTOS.