How webmethods server exactly creates server log everyday at 12:00 AM

webMethods, Every night at 12:00 AM achieves its logs and create new log.

Can any one help me how does this happen ?

This is a built in webMethods IS feature out of box that does create behind the scenes.

You need to check the WmRoot internal services and trace it at your own risk:

HTH,
RMG