The invention provides a large-pore composite plugging system and a preparation method thereof, belonging to the technical field of oil exploitation. The large-pore composite plugging system comprises amphoteric polyacrylamide solution with concentration of 0.2-0.5wt%, a flocculation agent solution and inorganic granules, wherein the flocculation agent solution is a cationic polymer solution with concentration of 0.2-0.5wt% or cationic surface active agent with concentration of 1-4wt%. The large-pore composite plugging system has the advantages of high elasticity, high plugging capability, movability and good thermal stability.