1) 经常性或习惯性的动作,常与表示频腮度的时间状语连用.
时间状语： every…, sometimes, at…, on Sunday
I leave home for school at 7 every morning.
2) 客观真理,客观存在,科学事实.
The earth moves around the sun. 不受时间限制的
Shanghai lies in the east of China. 客观存在
表示格言或警句中.
Pride goes before a fall. 骄者必败.
注意：此用法如果出现在宾语从句中,即使主句是过去时,从句谓语也要用一般现在时.
例：Columbus proved that the earth is round..
3) 现在时刻的状态、能力、性格、个性、特征.
I don't want so much.
Ann Wang writes good English but does not speak well.
比较：Now I put the sugar in the cup.
I am doing my homework now.
※4)由连词if unless before as soon as when once however 等引起的时间(条件、让步)状语从句,需要用一般现在时,表示将来时.
第一句用一般现在时,用于操作演示或指导说明的示范性动作,表示言行的瞬间动作.再如：Now watch me, I switch on the current and stand back. 第二句中的now是进行时的标志,表示正在进行的动作的客观状况,所以后句用一般现在时.
现在完成时用法解析
1.构成
现在完成时是由助动词 have(has)+动词的过去分词构成.助动词说明该谓语是属于现在时范围.它和主语的人称、数要保持一致.过去分词是主要的谓语动词,说明句子的意义.
2.用法
（1）表示动作发生在过去某个不确定的时间,但对现在留下了某种影响和结果.常被just、already、yet 等副词修饰.如：
-Have you had lunch yet? -Yes,I have. I've just had it.
你（已经）吃午饭了吗? 我刚刚吃过.（现在我不饿了）
（2）表示从过去某一时刻开始一直持续到现在的动作或状态.这个动作可能刚停止,可能仍然在进行.常带有for和since等表示一段时间的状语. 如：He has taught here since 1981
他自1981年就在这儿教书.（可能还要继续教）
I have't seen her for four years.
我有四年没见到她了.
（3）表示说话前发生过一次或多次的动作,现在成为一种经验,一般译为汉语“过”,常带有twice,ever,never,three times等时间状语.
如： I have been to Beijing twice.我去过北京二次.
3.现在完成时的时间状语
（1）现在完成时属于现在时范围,故不能和过去的时间状语连用.如：yesterday,last Sunday,in1990,three years ago等.但是,在强调动作产生的后果和影响时,可以和一些表示不确定的时间状语连用.
a. 用副词already和yet.already一般用于肯定句中,yet一般用于否定句和 疑问句中.如：We have already finished our homework.我们已完成作业了.
They haven't finished their homework yet.他们还没有完成作业.
b.用ever 和never.多用于否定或疑问句中,表示“曾经”或“从未“等. 如：-Have you ever been to the Great Wall?你曾经去过长城吗?
-I have never been to the Great Wall.我从未去过长城.
c.用表示到说话为止的过去时间状语,如just,before,up to now,the past few years等.
例如：I have seen her before,but I can not remember where.
我以前见过她,但记不起在哪里见过.
He has been there three times the last few days.
近几年他去过那里三次了.
d.用包括“现在”在内的时间状语,如：now,today,this morning(month,year,term)等.
例如：-Have you met him today?-No,I haven't.
今天你见过他吗?我 没有.
How many times have you been there this year?
今年你去过那里多少次?
（2）现在完成时可以和带有since或for等表示“一段时间”的状语连用,表示动作或状态从某一时刻开始,一直持续到现在.如：I haven't seen him for two years. 但是,像come,arrive,buy等终止性动词不能与表示“一段时间”的状语连用.要用,必须改为“be（在）”等延续性动词来表述.现归纳总结一下由非延续性动词到延续性动词的转换：
arrive→be here begin(start)→be on
die →be dead
fall ill(sick,asleep)→be ill(sick,asleep)
get up→be up go out →be out
finish →be over put on →wear 或be on
open →be open join →be in或 be a member of…
close →be closed go to school→be a student
borrow →keep buy →have
catch(a cold)→ have(a cold) get to know →know
begin to study→study come to work→work等
如：He has been a soldier for three years.他参军三年了.
His father has been dead for two years.他父亲去世二年了.
The film has been on for ten minutes.电影已开始十分钟了.
We have studied English for three years. 我们（开始）学英语已三年了.
4.现在完成时和一般过去时的区别
现在完成时和一般过去时都表示在过去完成的动作.但现在完成时强调的是这一动作与现在的关系.如对现在产生的结果或影响等,而一般过去时只表示动作在过去某一时刻发生,不表示和现在的关系.试比较：
I have lost my new book. 我把新书丢了.（现在还未找到）
I lost my new book yesterday. 我昨天把新书丢了.（昨天丢的,现在找到与否没说明）
5.几点注意事项
（1）have been(to)与have gone( to)的区别：have been(to)表示“去过某地（现在已经回来了）”,可用于各人称；have gone(to)表示“去某地了（说话时某人不在当地）”,常用于第三人称,前者可与once ,never,several times等连用,后者则不能.如：They have been to Beijing twice.他们去过北京两次.
He has gone to Beijing . 他去北京了.
（2）如单纯表示一段时间,或强调一段时间,虽有since一词,也不必用完成时.如：It is two years since his father died. =His father has been dead for two years.他父亲去世已有三年了.
（3）终止性动词现在完成时的否定式,已变成一种可以延续的状态,因此可以和表示一段时间的状语连用.
如：I haven't left here since 1997.自从1997年以来,我一直没有离开过这儿.