The hollow phenomenon about Sepat is analyzed in detail. It shows that the press ure after its landing was still much lower. Although theoretically speaking, the magnitude of this pressure is in typhoon level, the structure of typhoon eye w as destroyed, the wind power of central near by was low. The blank of cyclone ce nter in the radar echo chart is not typhoon eye. When Sepat was going to land, t here is no typhoon wall echo of intensively developing convective clouds, and th e structure of Sepat has been not integrated. Taiwan mountain destroys badly the lower structure of tropical cyclone over it, this also leads the appearance of dry tongue simultaneously. In a word, this hollow phenomenon is produced togethe r by the impact of the central mountain in Taiwan, the immixture of dry tongue a nd lower surface sea temperature.