The invention discloses a surfactant and a clean fracturing fluid and preparation methods thereof. The surfactant is brominated 1-methyl-4-alkyl imidazole and has a molecular formula of C26H59N2Br and a structural formula as described in the specification. The clean fracturing fluid comprises the following raw materials by weight: 5.60 to 10.50 parts of the surfactant, 0.15 to 0.40 part of an activator, 1.00 to 2.00 parts of counter ions and 87.10 to 93.25 parts of water. The preparation method for the surfactant is easy, reaction conditions are mild, and reaction yield is high. The clean fracturing fluid is prepared from the surfactant, the activator, the counter ions and water according to the above-mentioned weight parts and has the advantages of low cost, easy preparation, good resistance to high temperature, as high as 140 DEG C, and applicability to water in different areas. Moreover, the clean fracturing fluid has good compatibility with stratum water and can overcome and reduce damage caused by secondary precipitation.