I have unwrap this small asset in maya but after i finished adding the details ( which is not that much detail ) to the asset in z brush and i press the displacement maps it ruins the maps. it works when i do automatic map in maya but it will make the displacement horrible. i have no idea what could be the problem.
The created map looks like you have points outside the 0,0 to 1,1 UV space. What happens then is that when ZBrush goes to create the map, any points outside are “pulled” across the map, which results in exactly the sort of thing that you’re seeing.
Basically, a point that is at 1.1 would be treated as if it’s at 0.1 or a point that is at -0.9 would be treated as if it’s at 0.9.
The way to resolve the issue is simple: Keep all your points within the 0,0 to 1,1 UV space. 
Or if your intent is to create multiple texture maps then you would want to use MultiMap Exporter, which is included in ZBrush. It will create a separate map for each UV space.