Abstract: A statistical method of evaporation duct propagation loss is obtained based on the statistical features of evaporation duct and the propagation model. The statistical features of evaporation duct are acquired by Paulus-Jeske(PJ) model using marine observation data from 1982 to 1999. The median loss at S band of evaporation duct propagation is described using this method. Take the South China Sea for example, the distribution features of trans-horizon path loss and radio system availability are analyzed. The method can be used to analyze the availability of radio system and is confirmed by the distribution probability of the path loss of an evaporation duct propagation experiment.