on /upon doing sth 刚一做某事（就）；一……就
结构：介词+动名词（或者表示动作的名词）
功能：相当于as soon as引导的时间状语从句。这个结构表示它所表达的动作刚一发生或完成，句子谓语所表达的动作便接着发生。
例如：
我一到家就发现他们已经离开了。
On arriving home I discovered they had gone.
= As soon as I arrived home， I discovered they had gone.
= On my arrival home I discovered they had gone. ( on/upon doing必须注意，后面句子主语就是前面doing 动作的发出者。)
这些大学生一到村里就去帮助农民工作。
On arriving at the village, these college students went to help the farmers with their work.
=As soon as they arrived at the village, these college students went to help the farmers with their work.
= On their arrival at the village, these college students went to help the farmers with their work. ( on/upon doing必须注意，后面句子主语就是前面doing 动作的发出者。)
杰克一走出房间，就听到他的手机响了。
Upon going out of the room, Jack heard his cellphone ringing.
=As soon as he went out of the room, Jack heard his cellphone ringing.( on/upon doing必须
注意，后面句子主语就是前面doing 动作的发出者。)
再看几个经典例句：
On arriving at the shore, the girl struggled up the cliff towards the light she had seen.
一到岸边，女孩就朝着她看到灯光的方挣扎着向爬上悬崖。（新概念2，L33）
On entering a shop, he would ask for a new perfume called 'Scented Shadow' or for 'insoluble bath cubes'.
一走进商店，他就会提出要一种名叫“香影”的新型香水或什么“不溶浴皂”。（新概念3.L52）
Like Lenin. Mao Zedong, on coming to power, continued to develop his ideas in a context different from that within which he had operated while in opposition.
毛泽东，同列宁一样，一取得政权，便在与在野时不同的环境下继续发展他的思想。《剑桥中国史》