There are a few ways of expressing an ongoing action of a subject in Chinese. In this post, we are going to examine the differences between them.
Subject + 在／正在 + Verb + Object
This is used when you need to make a straightforward explanation of a physical action that has taken by a subject, what the subject is doing or what is happening to that subject at present.
There is no particular distinctions between 在，正在 expect that 正在 add a bit more emphasis to the sentence, it can be translated as ‘right now’.
wài miàn zài/zhèng zài xià yǔ
外面 在/正在 下 雨。 It is raining outside (right now).
It means exactly as what it says, ‘it is raining outside!’.
xiǎo míng zài/zhèng zài xǐ wǎn
小明 在／正在 洗 碗。 Xiao Ming is doing the dishes (right now).
This statement can be used, for instance, when you want to tell your friend ‘oh Xiao Ming is beside me, and he is just doing his dishes’. It’s a very straightforward description.
zài/zhèng zài chàng gē
Chelsea 在／正在 唱 歌。 Chelsea is singing (right now).
Verb ＋ 着
着 on the other hand， expresses a state of being. You use 着 in situations where you have a story to tell.
wài miàn xià zhe yǔ
外面下着雨… It is raining outside…
With this sentence, you can possibly add…
。。。但是丝毫影响不了她的心情。 But it does not affect her mood at all.
小明洗着碗… Xiao Ming is doing the dishes…
xiǎo míng bù tíng de xǐ zhe wǎn, bù zhī bù jué tiān jiù hēi le
Xiao Ming kept washing the dishes without stopping, unaware of that the day has gone dark.
Chelsea 唱着歌 Chàng zhe gē… Chelsea is singing…
chàng zhe tóng yī shǒu gē, xiǎng zhe tóng yī gè rén
Chelsea 唱着同一首歌， 想着同一个人。
Chelsea sings the same song, misses the same person.
You can see here, there is more story to it then simply a statement. Because 着 expresses a state of being, there is a reason to why a person is doing certain things.
Note that 在／正在， even 正 can also be used with 着：
wài miàn zài / zhèng zài / zhèng xià zhe yǔ
外面在／正在／正下着雨。。。 It is raining outside right at this moment..
xiǎo míng zài / zhèng zài/zhèng xǐ zhe wǎn
小明在／正在／正洗着碗。。。 Right now, Xiao Ming is doing the dishes…
zài/zhèng zài/zhèng chàng zhe gē
Chelsea在／正在／正唱着歌。。。 Chelsea is singing right now…
It is again, just to add a bit more emphasis to the sentence.
Here is also an additional point contributed by our lovely pirate ship member, where 着 and 在 can mean different things: