This paper analyzed the composition of urban forest in Nanjing briefly. The economic analysis was used to estimate the urban forest ecological value. The ecological value consists of manufacturing oxygen and fixing carboblic, purifying environment and sightseeing in forests. Nanjing street trees and forest resources in the scenic areas of Dr. Sun Yat-Sen’s Mausoleum were investigated. The economic value of urban forests was calculated. From the economics, it was a good suggestion to accelerate the development of urban forestry and ecological urban construction.