The invention discloses a method for treating and reusing fracturing backflow fluid of shale gas. The method comprises the following steps: (a) oxidizing Fe<2+> in original fracturing backflow fluid into Fe(OH)3, so as to obtain oxidized fracturing backflow fluid; (b) carrying out water quality analysis on the oxidized fracturing backflow fluid; (c) making comparison on the water quality of the oxidized fracturing backflow fluid and a reuse liquid preparation water quality requirement, and judging whether the concentrations of Ca<2+> and Mg<2+> in the oxidized fracturing backflow fluid of the shale gas are qualified; (d) if yes, sequentially carrying out coagulation, flocculation, sedimentation and filtration on the oxidized fracturing backflow fluid, and if no, sequentially carrying out coagulation-pH increase, ionic reaction, flocculation, sedimentation, filtration and pH value adjustment on the oxidized fracturing backflow fluid, so as to obtain treated fracturing backflow fluid; and (e) directly reusing the treated fracturing backflow fluid for liquid preparation or directly storing the treated fracturing backflow fluid. The method can adapt to the characteristics that the change of the water quality of the fracturing backflow fluid of the shale gas is large and reuse fracturing construction liquid preparation standards are different, and the instant continuous treatment can be realized.