thank you for your suggest!
device that I using is amazon kindle HDX 8.9’ 4th generation, the OS is FireOS 4.5.5.
this happens on the android device only, Editor is fine.
this problem can reproduce in a new project. my step is normal: first I new a empty Level as floor, than create a Cube Static Mesh, than add a material for cube, than add Directional Light. by the way, my PC’s OS is windows 10 x64.
I upload my test project on box, this problem can happen is this ue4 project:
https://app.box.com/s/x22yeds604f1qc1dhs66z0qme460ml20