Can anyone tell me, how can I use the cached shadows feature? Turning on&off?

You mean this?

https://docs.cryengine.com/display/SDKD ... ed+Shadows

Hi, I would check this https://docs.unrealengine.com/en-us/Eng ... amicLights it works also for exhibition design

Not really related to CRYENGINE though.

I wonder if it's something like Occlusion Mesh? (1)Is that possible to bake it like how we do with Occlusion Mesh? (2)Any way to turn it on/off or only flowgraph? (3) Does it only work in pure game mode(I tried but could not get anything so far)?

Crytek says that it exist, But does not give any tip to turn it on

Check the bottom page. There are cvars to switch on and off.