1.表示说话时正在进行或发生的动作

I'm babysitting my younger brother.

It's raining outside.

2.表示现阶段一直在进行或不断重复的动作，但说话时该动作并不一定在进行

He's watching an interesting TV play these days.

Are you teaching English in a school?

welcome home 欢迎回家

3. 表示即将发生的动作，适用于这种情况的动词主要有：go, come, leave, start, arrive 等,

I'm going home in half an hour.

The train is arriving soon.

4. 现在进行时和 always， usually， all the time 等连用时，表示一种经常、反复的动作，且说话人往往带有某种感情色彩(如赞扬、厌烦等)

She's always helping others.

You are always talking in class.