"速度变化图" can be translated into English as "velocity change graph" or "speed variation diagram".
"Velocity change graph" is more precise in a physics context, as "velocity" refers to both speed and direction (though in many cases where direction isn't changing significantly, it can be used interchangeably with "speed" for the graph's purpose).
"Speed variation diagram" is a more general term that focuses on the changes in speed, regardless of direction, and might be more commonly used in everyday language or non-technical contexts.
Choose the one that best fits the context in which you're using it.