The invention discloses a blockage removing agent for oilfields and a preparation method thereof, which comprises a pre-fluid, a main body fluid and a post-fluid with a mass ratio of 1:4:1; wherein, the pre-fluid includes hydrochloric acid, ethylene glycol Triaminepentaacetic acid amine, dodecyl dimethyl betaine, hydroxyethylidene diphosphonic acid, polyacrylamide, corrosion inhibitor, and the balance is water; the main liquid includes paraformaldehyde, ammonium chloride, Ammonium chloroacetate, ethylene glycol butyl ether, dodecyl dimethyl betaine, aminotriacetic acid, polyacrylamide, penetrating agent, corrosion inhibitor, and the balance is water; Acetic acid, sodium hypochlorite, butyl glycol ether, penetrating agent, corrosion inhibitor, and the balance is water. The present invention adopts the combination of acid + authigenic acid + oxidizing agent +, which can thoroughly degrade inorganic substances, biological bacteria clusters, metal corrosion products and high molecular polymers one by one, and then completely remove blockages in oil and water wells, achieving significant improvement The purpose of oil production.