Abstract: As an important ecological infrastructure of an urban area,whether a river system can work normally mainly depends on its structure and patterns,while the latter can be improved through the urban river system planning.By calculating and comparing the major indexes such as γ and α etc.of the spatial structure of a city's key river system before and after planning,we can find the changes of the structure and patterns of the river system,judge the rationality of the planning,and expose the essence of river system planning on improving the spatial structure of the local rivers and increasing the connectivity of the river system network.Taking Taicang's river system planning as an example,we calculate the γ and α and some other indexes of the current and planned river system.The results show that the indexes includingγandαincrease,which means that the structure and patterns of Taicang's river system are improved.The results of the four water-diversion areas show that the lower the value of the indexes of the current river system,the higher increasing range of the indexes of the planned river system,and there is remarkable spatial differece among the four areas.So once a river system plan of a city is worked out,the scale of the urban area should be considered firstly,and the next is the diversion-area scale.