The simplest way to answer this is to define each term,so you can see: A canyon is a deep valley with steep sides,think of the grand canyon most famously to visualise what this is. A gorge is a deep ravine,which usually has a river running through it - though this doesn't have to be the case. Finally a valley is any depression,usually of a certain length,in the surface of the land and often contains a river. So,a canyon is a specific type of valley,with particularly steep sides.A gorge is a particularly deep depression,and will usually contain a river. Canyon and gorge are somewhat interchangeable,depending on regional semantics,and describe a condition of land scoured or carved out by rivers (or wind),creating deep gouges in the earth of varying depths.A valley is usually a discernable low spot in the land,probably created by tectonic action or glacier movement. 正好我也在找这几个的区别,找到些自己看了顺便就贴一份, 参考资料：
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