Okay my question is : how to make a item to be on the character but if kill that character the item won't show in his inventory and you won't be able to take it ? If any one can help me please ! Thanks in advance !

Flag it as non-playable.

How to do that ?

Don't check the "Playable" checkbox when creating the item.

But if it's like in Oblivion, it will not be 100% reliable. Sometimes the game was going crazy and you were able to see in Inventory and equip "Unplayable" Item. I don't know if it's still the same in Skyrim.

You could simply remove it from your character, with OnDeath() for example.