"高低不平的地面" can be translated into English as "uneven ground" or "rough terrain", depending on the context and level of formality:
Uneven ground: This is a common and straightforward expression, suitable for most everyday situations. It emphasizes that the surface is not flat and has irregularities.
Rough terrain: This phrase is more specific and often used in contexts like hiking, outdoor exploration, or military operations. It conveys a sense that the ground is not only uneven but also potentially difficult to traverse.
Choose the one that best fits your specific context!