The invention discloses a treatment method of oil and gas field fracturing flow-back liquid. The treatment method comprises the following steps that (1) the flow-back liquid is added into a flocculation reaction tank containing a magnetic material, and then a composite treatment agent containing an oxidant, a pro-oxidant, a flocculant, a coagulant aid and a fungicide is added to carry out precipitation treatment, so that a solid-liquid mixture is obtained; and (2) the solid-liquid mixture obtained through precipitation treatment in the step (1) enters a precipitation tank through a water inlet pipe, suspended solids settle to enter a conical sludge precipitation bucket at the bottom of the precipitation tank to form precipitation slurry, liquid flows toward a buffer water tank from an overflow weir, enters a filter device after passing through the buffer water tank, and then flows out of the filter device to obtain purified water.