The construction of water－measuring devices in large and medium－sized irrigation areas is an important part of the comprehensive reform of agricultural water price． The setting principle of water － measuring devices and the arrangement of the water － measuring points directly affect the cost and efficiency of water metering in the irrigation area． In many large and medium－sized irrigation areas along the Beijing－Hangzhou Grand Canal，the irrigation areas along the Li Canal in Jiangsu Province were selected to study． The measurement and water demand were analyzed，and the setting principles of water－measuring devices were put forward． The Gaoyou irrigation area of national large irrigation area was taken as an example to give evidence，and the relevant suggestions on water－measuring devices were put forward．