Abstract: Valve-closing analysis is used to obtain the optimal valve-closing scheme in maintenance of water distribution networks，which is significant for water supply security. A new pipeline analysis model，unit-valve graph，is presented based on the traditional node-link graph model，which has much less features and concise topology. As a pseudo-dual graph of the original node-link graph，the unit valve graph classifies the network regions isolated by valves as vertexes，and takes valves as edges. An efficient isolated unit constructing algorithm is designed based on the node-link graph，which helps to build the unit-valve graph. Further more，an efficient valve closing algorithm based on the unit valve graph is developed. Experimental results show that the new algorithm has a remarkable advantage in terms of efficiency compared with the traditional algorithm and get a correct valve closing scheme even in the case of multi point construction.