Abstract: Evaporation duct is a crucial condition to realize beyond-line-of-sight (BLOS) radio propagation over the sea surface. Based on meteorological data and the Naval Postgraduate School (NPS) evaporation duct model, we find that the effect of evaporation duct is nearly permanent throughout the year in Beibu Gulf, South China Sea, where the evaporation duct heights (EDH) are approximately 6–18 m. In this sea area, we conducted propagation experiments over 40-km long BLOS links, using the E-band millimeter-wave (mm-wave), i.e., at 71–76 and 81–86 GHz. We find that the E-band waves can be well trapped in evaporation ducts, and their propagation losses are far below the simulated diffraction loss in a non-ducting atmosphere. Comparing the measured propagation losses to those predicted by the parabolic equation (PE) model, it is showed that the PE model can to some extent predict the losses of vertically-polarized wave propagation but significantly underestimates those of horizontally-polarized, when the model of sea surface roughness is introduced into the PE. In addition, E-band ducting propagation loss is much more sensitive to the variation of EDH, as compared to lower frequency bands. The research demonstrates a great potential of using the E-band for high-speed BLOS communications over sea. E-band ducting propagation modeling and across-sea communication system design may refer to the research results.