Aimed at the problems of imperfect agricultural water price formation mechanism and unscientific agricultural water price pricing in China，this paper analyzes the agricultural water price formation mechanism by using the method of theoretical analysis，and constructs the agricultural water supply cost water price model，then carries out the practice of agricultural water price formation mechanism in R county.The results show that agricultural water is a special commodity，and its formation mechanism should be the institutional arrangement of pricing and price adjustment under the market framework and government regulation，and the pricing should fully consider the water price cost and farmers'ability.Based on the calculation of agricultural water supply cost in R county，the water supply operation cost of artesian and water-carrying irrigation areas in R county are 462.30 yuan/hm2and 690.15 yuan/hm2respectively.In order to reduce the burden of farmers，the water price of artesian and water-carrying irrigation areas in R county are determined as 225 yuan/hm2and 300 yuan/hm2，and the difference is made up by the county finance.The research results can provide a theoretical basis for the pricing of agricultural water supply and the collection of water charges.