The urban permeable surface is an effective practice to conserve rainwater. This study presents a method to calculate the areas of the urban permeable surfaces and assess the benefits of the rainwater retained by them. As a case study in the Xigang District and the Zhongshan District of Dalian City,the areas of the urban permeable surfaces in 2005 were calculated based on the data from aerial photographic survey. Then the volume of the collected water in the year was obtained according to the annual rainfall amount,retaining ratio of the runoff,and infiltrating ratio of ground water. At last,the benefits of the rainwater retained by urban permeable surfaces were estimated using the economic and ecological benefit indexes. The main results from the study can be summarized as follows:(1) The total area of the permeable surfaces was 3 663.30 hm²,which was 51.5% of the total area of the study region. The area ratio of forestry land,grassland,and porous pavement was 6.5:1.3:1.0. (2) In virtue of the urban permeable surfaces,runoff was reduced by 1.69×107 m³,of which 5.0×106 m³ rainwater infiltrated into groundwater layer. Consequently,the total economic benefit of the retained rainwater was 1.4×106 RMB and the ecological benefit was 5.52×107 RMB. Moreover,great social benefit was generated due to controlled soil erosion and improved urban residential environment.