Method for preparing base fluid of fracturing fluid by using oil field well site waste water

The invention relates to a method for preparing a base fluid of a fracturing fluid by using oil field well site waste water, which comprises steps of pretreatment of oil field well site waste water and preparation of base fluid of the fracturing fluid, a flocculating agent in the pretreatment step is a mixture of poly aluminum ferric chloride and sodium carbonate according to mass ratio of 4-5:1; the preparation method of the base fluid of the fracturing fluid comprises the following steps: detecting mineralization of water after pretreatment; taking fresh water and adding guanidine glue, stirring and dissolving to prepare a guanidine glue solution, uniformly mixing the guanidine glue solution and water after pretreatment, when the water mineralization after pretreatment is 3000-5000ppm, the water volume ratio of the guanidine glue solution to water after pretreatment is 1:5-1:6; when the water mineralization after pretreatment is 5000-8000ppm, the water volume ratio of the guanidine glue solution to water after pretreatment is 1:4-5; when the water mineralization after pretreatment is 8000-10000ppm, the water volume ratio of the guanidine glue solution to water after pretreatment is 1:3-4.