The water accounting identity is an identical equation that reflects the intrinsic relationship among various elements in water accounting, which is the important theoretical basis for the subjects and account setting of water accounting and water balance sheet compiling. On the basis of the accrual system, the elements of the water accounting identity are discussed, and the basic concepts, confirmation conditions, components and calculation methods of each element are expounded. The water accounting system of New Coastal Area was then established accordingly to analyze and evaluate the water asset structure, water liability structure and water subject equity structure in recent years. The results showed that the total amount of water assets of New Coastal Area in 2018 is 68106×104 m3, an increase of 1.29% compared with 2017 and a decrease of 2.05% compared with 2016. The total amount of water liabilities is 7.60×104 m3, a decrease of 51.90% compared with 2017 and 75.08% compared with 2016. The total amount of water subject equity is 68098.40×104 m3, an increase of 1.30% compared with 2017, and a decrease of 2.01% compared with 2016. The water asset-liability ratio was 0.01%, a decrease of 0.01% compared with 2017 and 0.03% compared with 2016. The above results reflected the water resources management characteristics of New Coastal Area in 2018 such as high water resources optimization and allocation, stable water-related production activities, a small amount of water liabilities and high degree of water subject equity.