一、on用于具体的某一天(上、下午和晚上)前。在年份前用im,月份前
用in，年月前用in，季节前用in；在日前用on，月目前用on，年月日前用on，星期前用on，以Day结尾的节日前用om。例:
in 2008；in spring/summer/autumn/winter；in September；in September, 2008；on September 10th；on September 10th, 2003, on Monday/Tuesday；on Christmas Day; on Women' s Day,on National Day(在国庆节那天)
二、morning, afternoon, evening Hi this, that, next, last, tomorrow,yesterday等词限定时，则前面一律不用介词。例：
1、The boy was later for class this morning.
这个男孩今天早上上学迟到了。
2、Last Wednesday Lucy didn t go to school, because she was ill.
上个星期三露西没上学，因为她生病了。
3、I shall give a talk nert Thesday morning.
下周二上午我要作报告。
4、Tomorrow afernoon we are going to watch a football match.
明天下午我们将看一场足球赛。
5、There was an accident on this street that afternoon.
那天下午在这条街上发生了一起车祸。
三、在时间点前常用介词at，例：
at six o clock; at half past eight, at ten to nine; at a quarter pasteleven; at twelve twenty.
四、其他情况。例：
1、My family moved to France in that summer.
那个夏天我们家搬到了法国。( in that summer表特指)
2、How many minutes are there in an hour?一小时有多少分钟? (in an hour表泛指)
3、What day is it todav?
今天星期几今天是什么节日?
It is Tuesday/Children’sDay.
今天是星期二/儿童节。(I指 Tuesday或 Children's day故Tuesday或 Children Day前不加on)
4、My birthday is on October Ist.
10月1日是我的生日。( My birthday前不加on）
5、Let s make it nine forty.
我们把时间定在9:40吧。(it指 nineforty,故 nine forty前不加at)
6、It rained heavily last night.
昨晚雨下得很大。( last night不能写成yesterday night)
7、We’Il leave here tomorrow morning.
明早我们将离开这里。( tomorrow morning不能写成 next morning)