After the middle route of the South-to-North Water Transfer Project was officially put into operation, it effectively alleviated the shortage of water resources in Beijing-Tianjin-North China. It has become an indispensable main water source in the receiving area. The South-to-North Water Transfer Project is a single-line water transmission, and many uncertain factors may cause water transmission interruption. In order to improve the water supply guarantee of the South-to-North Water Transfer Middle Line Phase I Project, it is very necessary to carry out the emergency water supply research of the built reservoirs along the main canal connection. If the emergency water supply of the reservoir is transferred across regions, the water supply cost needs to be calculated. On the basis of determining the technical scheme of the connection between the reservoir and the main channel, this paper establishes a cross-regional transfer water supply cost model for the emergency water supply of the reservoir, and proposes a multi-source and multi-objective cost water price accounting system. The cost of emergency storage and water supply of the built reservoir includes the comprehensive cost of the raw water of the built reservoir, the cost of the interconnection project, and the cost of water transmission in the main channel section. Among them, the comprehensive cost of raw water for reservoir water supply is divided into two parts: the cost of raw water production of the built reservoir and the compensation for agricultural water consumption; The cost of the Unicom project can be accounted for separately according to three different schemes: no depreciation, depreciation by year and depreciation by time; The water delivery cost of the main channel section is calculated by the water price measured at the water supply target gate and the water price measured at the main channel gate of the reservoir. When multiple reservoirs supply water jointly, the water supply cost is calculated comprehensively and weighted. Research has shown that, without considering depreciation, the raw water cost of each reservoir ranges from 0.02 to 0.44 Yuan/m³, the cost of interconnecting projects ranges from 0.04 to 2.17 Yuan/m³, and the comprehensive water supply cost of multi water source joint scheduling for different water users ranges from 0.60 to 1.71 Yuan/m³. This article analyzes the cost water prices of different schemes based on typical examples, providing a reference basis for calculating the cost water prices of multi source and multi-objective emergency water supply.