on the top of 是指在具体物体的顶部
如：
The pagoda stands alone on the top of the hill.
那宝塔孤零零地坐落在山顶上.
The skin exactly on the top of my head pains.
我头上正好位于头顶的那块皮肤很痛.
而 on top of 即可以表示在有形的物体上方,也可以表示不具体的某事物的顶端,而且还具有其它的意思.如
There is a bird on top of the house
房子顶上有只鸟.
I am on top of the world.
我高兴到了极点.
This work is getting on top of me.
这件工作我无法胜任了.
On top of this,several other benefits are being offered.
除此以外,其它几项好处正在出现