The invention discloses a high-strength sealing plugging agent, which comprises, by mass, 15-20% of a fluorenyl epoxy resin, 10-12% of an epoxy resin, 10-12% of an alkaline phenol formaldehyde resin,20-30% of a solvent, 4-5% of a coupling agent, 15-20% of a filler, 4-5% of a degassing agent and 4-5% of a curing agent, wherein the degassing agent is a modified calcium-based degassing agent, the fluorenyl epoxy resin is 9,9-bis[(2,3-epoxypropoxy)phenyl]fluorene, the filler is a compounding agent prepared from superfine cement powder and PVA fibers according to a mass ratio of 4:1-3:1, and the curing agent is prepared by compounding benzophenone imine and 9,9-bis(4-aminophenyl)fluorene according to a mass ratio of 1:1. According to the invention, the plugging agent can effectively plug crackand micro-crack leakage layers of oil wells, gas wells and water wells, has characteristics of good sealing property, high compressive strength, strong scouring resistance, good operability and highplugging success rate, and particularly has outstanding effect in gas well micro-crack plugging treatment.