The invention discloses a composite flocculating agent used for flotation of tailings of a micro-grained gold deposit and an application method thereof, and belongs to the field of gold ore flotation. The method comprises the following steps of flotation tailing blending, stage agent addition, tailing settling and return water recycling/tailing pond removing through underflow. The composite flocculating agent has the beneficial effects that the technical scheme is adopted for accelerating settling of the micro-grained flotation tailings in a thickener, the solid content of overflow water of the thickener is lowered, and the clarity of the overflow water is increased; the return water utilization rate of flotation tailings in a concentrating mill is 65.53%-73.86%, the usage amount of new water is reduced, the problem that the new water of the concentrating mill is insufficient is effectively solved, and the return water utilization rate is increased; the return water use ratio is increased, after the return water returns to an ore separation system, residual flotation reagents in the return water are fully used, the usage amount of various flotation reagents can be obviously reduced through reagent system optimization, and the production cost is effectively reduced; the solid concentration of the flotation tailings discharged into a tailing pond is increased, the tailing conveying energy consumption and tailing pond safety risks are reduced, and the composite flocculating agent is environmentally friendly.