“Huge swell” is the main cause of damage to La Libertad Pier in El Salvador. We use the NOAA global reanalysis wave data to analyze the characteristics of high waves in the project sea area. The results show that there are two super high waves every year，similar to “tsunami-like” swell，which come from the South Pacific（east of Australia）and the South Ocean，propagate across the ocean along the great circle path，and reach El Salvador for about 12 to 20 days. When the high wave propagates into the shallow water area，wave directions change to S direction due to the terrain refraction effect and wave heights increase sharply due to the shallow water effect until it is broken. According to the propagation characteristics of long-period swell，the high wave warning can be carried out in advance to guide the construction and wharf operation.