how to make a limit for the loop cut tool are there any way for making the loop cut not going to certain vertex group in the mesh ? as you see in the image when i click on ctrl + r the loop cut go through all the character from her head to her foot but i want to not add any new loop cut to the character head so are there any way for that ?
Switch to Face Select Mode, select the faces you want to keep and hide them with H. Then do your loop cut. After that, reveal your faces with ALTH. 

The loopcut will have added a new vertex but it will not have cut through. So, if you have hidden some quads, you will get an ngon. Not ideal but you can retopologize it later.