In order to cater to the growing demand for data communication in the 5G and 6G era, aiming at the development trend of ultra high speed Ethernet multi service support, flexible speed and IP optical fusion networking at this stage, this paper studies the protocol specifications of flexible ethernet(FlexE), including FlexE basic structure, overhead frame definition and Calendar mechanism. On this basis, a functional model for mapping user data of different rates in the media access control(MAC) layer to the physical layer is proposed, and a time slot allocation algorithm based on the Calendar mechanism is studied.