I know brush can be mirrored
but how to mirror hair guide in proper way while the head is also symmetric
I used mirror node after groom node ,but the guides no longer attach the head

I think that currently, if you want perfect symmetric hair guides, you have to set the Mode in your Guide Groom node to “Guide per Point”. Then, if your topology is also perfectly symmetrical, you'll get symmetric guides.
If there is a way to get guides symmetry with “Scatter on Surface” mode, I'd also be interested to know how might that be achieved.