Abstract: In order to understand the ability of forest land to improve soil properties, at the Dafeng forest farm of the muddy sea-coast in northern Jiangsu Province, pure forest of Populus tomentos at the different ages （6a、7a、16a、19a）, and 16-year-old pure forest of Metasequoia glyptostroboides were selected for the study and the beach land of Phragmites communis was selected as control group, the physical and chemical properties of of soil were studied, such as bulk density, organic matter content, total nitrogen content, total phosphorus content and pH value of soil. The effect of the different age in the same species, the different species in the same age, the forest land, the beach land of Phragmites communis on the physical and chemical properties of soil was discussed. The paper gives out some research results as follows. 1) the Populus tomentos pure forest has a good ability to improve soil properties, such as reducing bulk density and pH value, increasing the content of organic matter, total nitrogen and total phosphorus. 2) The ability of soil improvement is closely related to forest age and root distribution. The higher forest age is, the stronger the ability of soil improvement is. With the increased soil depth, root number decreased gradually, which leads to the reduction of ability of improving soil properties layer by layer.