We give a general expression of the dielectric constant tensor in orientational orders in the applied static or low-frequency electric field for the semi-two-dimensional monolayer films with C-infinity upsilon symmetry. The dielectric anisotropic orientational tensor and orientational polarization tensor are derived in orientational order parameters. The nonlinear electro-optical Pockels effect including the local-field influence is also discussed using the orientational orders. A numerical calculation result shows that the first orientational order parameter S-1 is a destructive order while the second orientational orientational order parameter S-2 is a constructive one to the dielectric constant in the normal direction of monolayer films.