After I place a UGUI panel and a scroll view control in my app, everything become slow. Why Unity UI made a low fps?
What sort of shader are you using for the UI? I wouldn't recommend using the Standard shader since its not really optimized for mobile. There is another thread here with advise/links that should help: http://forum.unity3d.com/threads/unity-shader-lighting-performance-tips-for-hololens.411691/