Thanks for your reply 
I found that this maybe a bug caused by the engine’s not setting the engine.disableUniformBuffers property correctly in mobile mode.
When I visit my project in my browser in normal mode, after I create my engine,the engine.disableUniformBuffers is true,and it perform well.
But when I change my browser to mobile mode, the engine.disableUniformBuffers value become false,which cause a bad performance 
.
And I think this is similar to this bug:
https://forum.babylonjs.com/t/loading-time-performance-regression/28504/4
(Related Commit)
And my solution is change this value to true manully after I create my engine.(now it performace well!!!)
