1、at，on和in是表示时间的常用介词，用好这三个时间介词，可以先抓住一个大的原则，即at某时刻, on某天, in某段时间，时间的跨度是由小到大。选用介词at的场合：用于钟点前at ten oclockat a quarter to six用于时刻前at noon/night/midnight(半夜)at sunrise(日出时)at dusk(黄昏)at dawn/daybreak (黎明)eg:We will leave at daybreak.我们将在黎明时动身。用于表示进餐时间。如：at breakfast/lunch/supper(在早餐时/午餐时/晚餐时)eg:He drinks
2、tea at breakfast.他在早餐时饮茶。用于表示年龄时。如：at 14 (=at the age of 14在14岁)eg:He left home at the age of 16.他十六岁离开了家。用于一些固定短语或习惯搭配中。如：at Christmasat New Yearat Thanksgiving(感恩节)at the beginning/end of last monthat the moment/ at that timeat this time of dayat a bad time of yearat first(起初)at last(终于)选用介词on的场合：
3、用于星期、日期(包括该天的各部分)前on Sundays/weekdayson Monday morning / afternoon / eveningeg:Im flying home on Sunday afternoon.我星期四下午乘飞机回家。“在周末”既可以说at weekends，也可以说on weekendseg:I often go fishing on/ at weekends.我经常在周末去钓鱼。用于morning/afternoon/evening/night/day前，此时这类名词前多有修饰语或带有of等引起的后置修饰语，指具体的或不具体的某一日on a cold af
4、ternoonon the night of October 1, 1997on the first dayon his birthdayon Friday afternoon用于公共节假日前：on Teachers Dayon Christmas DayEveon National Day特别注意：at，on都可用来表示“节假日”，但at侧重指“休假的时节”，而不是指具体的哪一天；on侧重指具体的时日，与它连用的短语中多含“Day”at New Year(在新年期间) at Christmas (在圣诞节期间)on New Years Day(在元旦那天) on Christmas Day
5、(在圣诞节)选用介词in的场合：用于泛指一天的上午、下午、傍晚如：in the morning/afternoon/evening/night用于某个较长的时间，像世纪、朝代、年、月、季节in Marchin springin 1997in the twenty-first century(在二十一世纪)in ones fifties(在某人50多岁时)用于表示“从现在起，多久以后或多长时间内”的短语之前Shell see me again in a weeks time.一周后她再来看我。I can draw a beautiful horse in five minutes.我可以在五分钟
6、内画好一匹好看的马。There are seven days in a week.一周有七天。省略介词的情况：有些情况，既不用in，也不用on和at，时间前面可不带介词。家长可以让孩子认清标志，注意哪些情况下要省略介词，避免画蛇添足。next，last，this，that与时间名词连用作状语时Were going to work on a farm next Sunday.下个星期天，我们要去农场劳动。They visited the Great Wall last year.去年他们参观了长城。today, tomorrow, yesterday, the day before yesterday,等之前Are you free tomorrow night? 明晚你有空吗?Where did you go the day before yesterday? 前天你去哪儿了?
