Abstract: The major ecological site factors controlling the sensitivity of sub-tropical ecosystems to acidic deposition have been discussed.The index system of the relative sensitivity class has been put forward.The relative sensitivity class of ecosystems in East China has been mapped,based on a lot of information.The results indicated that the sensitivity of ecosystems in the studied regions has a significant difference,the most sensitive and sensitive areas account for more than 1/3 of the total areas in the region,mainly distributed in Fujian province,Zejiang province and Jiangxi province.