Abstract: The total cross section of the process mu- mu+ > vm vm~ ttH has strong dependence on the CP phase (xi) of the top Yukawa coupling, where the ratio of xi=pi and xi=0 (SM) grows to 630 at rts=30 TeV, 3300 at 100 TeV. We study the cause of the strong energy dependence and identied its origin as the (E/mW)2 growth of the weak boson fusion sub-amplitudes, WL- WL+ > ttH, when the two W's are longitudinally polarized. We repeat the study in the SMEFT framework where the EW gauge invariance is manifest, and find that the highest energy cross section is reduced to a quarter of the complex top Yukawa model result, with the same energy power. By applying the Goldstone boson (GB) equivalence theorem, we identied the origin of this strong energy growth of the SMEFT amplitudes as the contact dimension-6 pi-pi+ttH vertex, where pi^+- denotes the GB of W^+-. We obtain the Unitarity bound on the coecient of the SMEFT operator by using the optical theorem.