The invention discloses a high-efficiency concentrated inorganic boron crosslinked fluid and a preparation method thereof. The crosslinked fluid is prepared by mixing a component A and a component B in a weight ratio of 100:10, wherein the component A is composed of the following raw materials in parts by weight: 20-50 parts of boron, 30-55 parts of oxidizer, 1-8 parts of stabilizer, 10-20 parts of dispersing agent and 9-22.5 parts of water; the component B is composed of the following raw materials in parts by weight: 5 parts of pH regulator and 1-2.5 parts of water; and the pH regulator is NaOH or triethanolamine. The preparation method comprises the following steps: adding the water into a reaction kettle according to parts by weight, adding the borax, oxidizer and stabilizer while stirring, carrying out thermostatic reaction at 60 DEG C for 60 minutes, adding the dispersing agent, uniformly stirring to obtain a fluid A, and evenly mixing the fluid A and the pH regulator in the ratio of 100:10 to obtain the high-efficiency concentrated inorganic boron crosslinked fluid. The crosslinked fluid disclosed by the invention has the characteristic of high concentration; and the effective boron content in the crosslinked fluid is 30-50%, so that the effective concentration of boron in the crosslinked fluid is obviously enhanced, thereby obviously improving the transportation and use controllability.