The invention discloses an efficient composite water treatment agent and a preparation method thereof. The preparation method comprises the following steps that 1, raw materials of polyacrylamide, polyaluminum chloride, polymerized ferrous sulfate, palygorskite, a synergist and activated carbon are weighed; 2, the raw materials are evenly mixed to obtain the efficient composite water treatment agent. According to the efficient composite water treatment agent and the preparation method thereof, combination of the organic matter and the inorganic matters is used for sewage purification, the efficient composite water treatment agent has multiple kinds of medicine effects and functions, the flocculating settling speed is high, the flocculating settling effect is good, moreover, the preparationtechnology is simple and low in cost and can be widely used for treating various kinds of industrial sewage and municipal sewage, not only is the quality of sewage treatment improved, but also the cost of the water treatment agent is reduced, the treatment effect is stable, and thus the efficient composite water treatment agent and the preparation method thereof are suitable for application and popularization.