Thank you for your prompt reply!
The data on my side is the surface mesh.Because the VTP file extracts the surface mesh of VTK for storage (in other words, the model rendered by the VTP file is an empty shell, only the surface data)
This cut model is divided into two parts, one is the cross section face and the other is the cross section body.
I only need to think about the cross section body now, how to cut and show the color I want.