The purpose of this study is to clarify the environmental changes and human activities before and after the fortification of the Seongsan Sanseong Fortress (hereinafter mountain fortress) in Haman through using pollen analysis. For this purpose, samples were taken at the Tr-2 site in the Warm-temperate forest. The results of the analysis are as follow. ① Before and after the fortification of the mountain fortress, the area around it has changed from a broad-leaved forest (The HS-I period) into a deciduous broad-leaved forest (The HS-II period) and finally into a the mixed conifer and deciduous broad-leaved forest (The HS-III period). ② The HS-I period (before the middle of the 6th century, compared to the nationwide pollen zone RIIIa during the Postglacial) was covered with cool-temperate southern forests(including some species of Warm-temperate trees) and was very similar to the current climate environment during the Gaya period before the fortification. ③ The HS-II period (mid to late 6th century, pollen zone RIIIa) was covered with typical cool-temperate southern forests after the fortification and the temperature was slightly lower than the first stage. ④ The HS-III period (7th~8th century/9th century, pollen zone RIIIb) is an era of clear human interference, causing the destruction of forests in earnest and paving an active agricultural life.