on：表面有接触，A在B上面，如书在桌上，书和桌子相接触。above：无接触，泛指上方，高于，如鸟在水面上，鸟相对于水来讲位置处于上方。over：正上方、垂直上方，可接触，可不接触，B在A笼罩范围之内（A灯在上方，B下方的在灯光范围内）。
Above的用法
1.PREP介词…上方;高于Apartment 46 was a quiet apartment, unlike the one above it...
和它楼上的那间不同，46号公寓很安静。
He was staring into the mirror above him.
他盯着在他上方的镜子。
2.ADV副词上述;在上文【搭配模式】：ADJ Several conclusions could be drawn from the results described above...
从上文描述的结果中可以得出几个结论。
Full details are in the table above.
详细信息请见上文表格。
Above也是个名词
For additional information, contact any of the above.
如需更多信息，可与以上任何一处联系。
Above也是形容词
For a copy of their brochure, write to the above address.
欲索取其宣传册，请写信至以上地址。
3.PREP 介词（数量或度量）在…以上，超过 If an amount or measurement is above a particular level, it is greater than that level.
The temperature crept up to just above 40 degrees...
温度攀升至40度出头。
Victoria Falls has had above average levels of rainfall this year...
维多利亚瀑布今年的降雨量超过了平均水平。
These plants must be stored in the light at above freezing temperature...
这些植物必须放置于零度以上光照充足的地方。
Government spending is planned to rise 3 per cent above inflation.
政府开支拟订高出通货膨胀3个百分点。