left-handedness
 

When I import mesh to FLUENT and check, it shows "Zone 12: 12314572 right-handed, 165 left-handed". In Gmabit, when i check the volume gird, no problem '0 out of 1 meshed volume failed mesh check for inverted elements'.

When I type command in FLUENT, "grid/modify-zones/repair-face-handedness", it says "Left-handed faces can't be converted to right-handed faces.All face nodes have the right order, but the mesh probably contains non-convex cells."

What shall I do? How to solve the error? the type of the mesh is tetrahedral

It just means you have some cell with negative volume. For tetrahedral meshes, this typically occurs when you have some poor quality cells, maybe trying to resolve high curvature while not using enough elements causing them to fold over themselves.

Just go through your mesh and make sure your cells aren't highly skewed and increase grid resolution in critical areas. Due to the small number of left-handed cells, I'm assuming they are all in a region that simply wasn't meshed properly resulting in poor cell quality.