Abstract: Study on the fade slope characteristics of the transmission loss has important significance for the design and the evaluation of the microwave over-the-horizon systems which Fade Mitigation Techniques may be implemented. Transmission loss measurements at 14.1 GHz have recently been made on the oversea paths in the areas of the Yellow sea and the Bohai sea of China. The availability of the data is analyzed combining with the troposcatter parabolic equation method, the Advance Refractive Effects Prediction System (AREPS) and the local meteorological data. Then, this paper focuses on the study of the fade slope characteristics of the transmission loss. The stability of the trans-horizon microwave signal, which propagated on oversea with the duct, the super-refractive, the troposcatter and the hybrid mechanism, has also been analyzed with the fade slope characteristics of transmission loss.