1.“on” 表示某物位于另一物体的表面上，两者之间有接触。比如：

　　The book is on the table.

　　书在桌子上。

　　The spider is walking on the ceiling.

蜘蛛在天花板上爬行。

On the floor above the theatre are the deans' offices.=

The deans’ offices are located just over the theater.

院长办公室就在剧院的正上方。

2.above作介词表示“在...上方”，泛指的是一个范围。表示某物位置高于另一物，但不一定在正上方，也不与其宾语相接触。比如：

The sun rose above the horizon.

太阳升到地平线以上。

The jet flew above the clouds.

喷气式飞机在云层上面飞行。

The moon was now above the trees in the east.

月亮挂在东方的树梢上。

　　The plane flew above the clouds.

飞机在云层上飞行。

　　The hills above the valley are bare rock.

河谷上面的山是光秃秃的岩石。

The water came above our knees.

水淹过了我们的膝盖。

当表示“高于某个抽象的水平”应该用above,如：

The mountain is 1,000 feet above sea level.

这座山高海拔一千英尺。

Situated at an altitude of 7 ,600 feet above sea level and only 15 degrees north of the equator, Kagnew Station occupies a unique position in the communications world. ( 托福真题)

Kagnew站位于海拔7600英尺，赤道以北仅15度，在通信领域占据着独特的地位。

They finished the year six places above their local rivals.

这一年结束，他们的排名比当地竞争对手超前六个名次。

His work is well above the average.

他的工作大大超过一般水平。

当表示某个具体温度是零上多少度时,也只能使用 above:

The temperature is three degrees above zero.

温度是零上三度。

It's a sunny late winter day, just a few degrees above zero

那是晚冬阳光明媚的一天，温度只有零上几度。

如果表示温度在某个度数以上,则既可使用above,也可使用over:

The temperature is above/over 30℃. 温度是摄氏三十度以上。

By mid-morning, the temperature was already above/over 100 degrees Fahrenheit.

到早上10点钟，温度已经超过100华氏度了。

可表示（数目、数量、水平、年龄）超过，多于，大于

Inflation is above 6%.

通货膨胀超过6%。

Temperatures have been above average.

气温一直比平均温度高。

We cannot accept children above the age of 10.

我们不能接受10岁以上的儿童。

3.over作介词基本意义表示“在...上方”，表示准确的位置，物体间可接触，可不接触;比如：

The light hangs over the desk.

灯在书桌上方。

There was a lamp hanging over the table.

桌子上方吊着一盏灯。

Jane held the umbrella over her head.

简把伞举在头上。

They held a large umbrella over her.

他们给她撑起一把大伞。

The balcony juts out over the street.

阳台伸出在街道上方。

She put a blanket over the sleeping child.

她给熟睡的孩子盖上毯子。

His hair fell over his brow instead of being brushed straight back.

他的头发没有整齐地往后梳，而是搭在前额。

He wore an overcoat over his suit.

他在西服外面再加了一件大衣。

She put her hand over her mouth to stop herself from screaming.

她用手捂住嘴，以免叫出声来。

On the floor above the theatre are the deans' offices.=

The deans’ offices are located just over the theater.

院长办公室就在剧院的正上方。

He lives on the floor above/over us.

他住在我们楼上。

We live above/over a small bookstore.

我们住在一家小书店的楼上。

可表示多于、超过（某时间、数量、花费等）

more than a particular time, amount, cost, etc.

over 3 million copies sold

售出三百多万册

She stayed in Lagos for over a month.

她在拉各斯逗留了一个多月。

He's over sixty.

他六十多岁了。