Gridgen Symmetry layer Height
 

I want to use symmetry option while creating a block. but my domain in structured and symmetry option is nor working for structured domain

Extruding a structured block?
 

If you are extruding a structured block, use the adjacent grid boundary condition to make the extruded grid match the symmetry grid.

Actually my question was that in my unstructured block there are also some structured domains as im trying to make hybrid grid.Unstructured for complicated geometry parts and structured for other parts.Now the situation is that my symmetry domains are the structured domains in the block so when i run the solver and try to give symmetry layer height to those domains they remain as isotropic.But if i try the same with those domains as unstructured it works why is this? and how do i make it work in my situation?

Can't use structured domains for T-Rex symmetry
 

Sounds like you are making a T-Rex grid, which is extruded anisotropic tetrahedra. Because tetrahedra only have triangular faces, you can only use a domain with triangles on it as a symmetry boundary condition for a T-Rex extrusion.

You might try a prism extrusion. The prisms have quadrilateral faces on the sides, so you can use a structured domain as the matched boundary (adjacent grid boundary condition).