"图形表示法" can be translated into English as "graphical representation method" or simply "graphical representation" (depending on the context, where "method" may be omitted if the focus is on the representation itself rather than the specific technique of creating it).
Graphical representation method: Emphasizes the systematic or procedural approach to representing data or concepts graphically.
Graphical representation: Focuses more on the end result or the act of representing something visually.
Both are correct, and the choice between them depends on the specific nuance you want to convey.