The invention provides a water block removing agent and a preparation method thereof. The water block removing agent comprises the following substances by weight: 10 to 12% of a weak hydrophilizing agent, 8 to 10% of an acid-soluble oxidizing agent and 0.5 to 1.5% of a corrosion inhibitor, with the balance being water. The water block removing agent is applicable to Changqing ancient low-permeability sandstone gas-bearing formations, enables strong hydrophilicity of low-permeability sandstone gas reservoirs to be changed into weak hydrophilicity, eliminates capillary force in reservoir strata, enters a part of solid-phase particles and cellulose via acid dissolution, decomposes macro-molecular polymers via oxidation, removes blocking and improves gas flooding efficiency in water removal; thus, the restoration ratio of rock core permeability is obviously improved.