With the inclusion of satellite Internet as the information infrastructure in China's“new infrastructure”category, relevant domestic industries and scientific research institutes have successively carried out the design of broadband low earth orbit (LEO) constellation sys?tems and key technical research. As the core technology for the satellite-to-ground network communications of a broadband LEO constellation system, routing technology is extremely im?portant for the efficient and reliable transmission of various service data. Focusing on the two important broadband LEO constellation systems in China, in-depth analysis and simulation of the high dynamics of the satellite-to-ground satellites are conducted in this paper to obtain more accurate network topology changes and characteristics; then the adaptability of the ground standard IP routing protocol to the broadband LEO constellation system is analyzed, and an LEO constellation simulation scenario is built with the Opnet software. The simulation results of the convergence performance of the standard IP routing protocol are produced. The results show that the IP protocol does not perform well for LEO satellite constellation net?works. Based on the studies, some solutions are proposed to take full advantages of the charac?teristics of LEO satellite systems. These can also provide a reference for the choice of inter-satellite routing architecture and protocol technology for broadband LEO constellation in the future development.