The invention discloses a flushing fluid, a preparation method thereof, and a flushing fluid for deep water well cementing, which belong to the field of well cementing operations. The flushing solution includes: diluent and cleaning agent; the mass ratio of diluent to cleaning agent is 75-95:18-24; the diluent includes: water, sulfonated tannin, sodium hexametaphosphate, and hydroxyethyl cellulose; The mass ratio of water, sulfonated tannin, sodium hexametaphosphate, and hydroxyethyl cellulose is 75-85:8-12:6-10:1-4; cleaning agents include: ethylene glycol, fatty alcohol polyoxyethylene Ether, octylphenol polyoxyethylene ether; mass ratio of ethylene glycol, fatty alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether is 65-75:15-25:5-15. When the flushing fluid is applied to the flushing fluid for deepwater well cementing, it can dilute the mixing section with drilling fluid and / or cement slurry, effectively prevent cement slurry and drilling fluid from mixing, avoid cement slurry flocculation, shorten the thickening time, and ensure mixing The section has good rheological properties, effectively flushes the virtual mud cake of drilling fluid, casing and borehole wall annulus, and can be applied in deepwater cementing operations at 0-30°C.