The invention relates to a strong wall-building composite plugging agent, which is applied to plugging of an oilfield void well, a cracked stratum, a loss well and a casing-damaged leakage well. The composite plugging agent comprises the following components: 0.1 to 2.0 percent of natural branch-chain fiber, 0.1 to 2.0 percent of synthetic straight-chain fiber, 50 to 80 percent of oil-well cement, 5.0 to 30.0 percent of superfine cement and 5.0 to 30.0 percent of silicon dust or/and 0.01 to 2.0 percent of retarding agent, wherein the natural branch-chain fiber is dried cotton fiber from whichseeds and husks are removed, and the water content thereof is less than or equal to 0.1 percent; the synthetic straight-chain fiber is synthetic polypropylene fiber, the water content is less than orequal to 0.1 percent, the diameter of single filaments is 0.05 to 0.5 millimeters, and the length is 5 to 50 millimeters; and the retarding agent is calcium lignosulphonate. The composite plugging agent has the advantages of stable system, strong wall-building capability, strong plugging capability, adjustable plugging depth and small using amount; the plugging resists 25MPa pressure; and the success rate of one-time construction reaches over 90 percent.