How to say that there is a poster located on the wall of my room ?
How to say that ?
By the way , Is "on the wall" correct ? what about room , in or on ?
Posters hang on the wall. You got that right.
As for where that particular wall is, you can use either "of" or "in":
Sometimes there's a "right" preposition to use, and sometimes more than one can be used and the meaning of the sentence doesn't change. You've given a sentence where there's an obvious choice for the first preposition, but wiggle room with regards to the second.
Yes, we hang posters "on the wall", although I can see how a beginner might be unsure of that. See meaning 1c at Macmillan:
I would suggest changing "of" to "in." Also, adding "located" is valid, but unnecessary.
Not very specific
Not specific about where in the room:
In English, yes, you should use the preposition "on" when hanging things "on" walls. Things don't go "in" the wall, unless they're actually encased in it, like water pipes or electrical wires, or perhaps a safe that's actually embedded "in" the wall.
You'd use "in" for "in the room" because it is a space you can go "in"to. You can't go "on" a room (unless you're standing on top of it, and even then it sounds weird).
You can say:
and 99% of native speakers will know what you mean. If your goal is to be able to communicate your ideas in English, that sentence might be all you want. If you want to use more natural English, you could say
There is a poster hanging on the wall of my room.
which is close to your sentence in construction.