Dose watching American TV can improve english?

ya people believe that but frankly speaking American movie channel helps you understand their accent rather than improve your vocabulary.So I think you should watch news channels and informative channels which helps in increasing vocabulary and makes you capable to express your views firmly.

it is helpful in the times when you need to hear the sounds of some words and to tell it but i think that it is really hard to learn the language just from watching tv or films i think that it is stupid because there are so much grammar to learn and writing is important too...

You will definitely learn English by watching American television, but that doesn't mean it will be proper English, with correct vernacular. But even shows where people don't speak English properly, you might still pick up on helpful things. There are many phrases American people say that are common throughout English speaking countries. They aren't listed of course in an English course. But it is something that might help one fit in if ever put into a conversation where "slang" is spoken.

Sometimes it helps, sometimes it harms. Some movies have wrong grammars in the show. Try to watch educational shows in discovery channel, and some news channels. Informative channels have better grammars than movies. and more realistic.