The invention relates to a phosphate anhydrous fracturing fluid gelling agent and a preparation method thereof. The preparation method comprises the following steps: by taking phosphoric acid, phosphorus pentoxide and C12-C18 alcohol as raw materials, reacting for 4-6 hours at a temperature of 60-70 DEG C so as to obtain a monoalkyl phosphate ester, wherein the molar ratio of phosphoric acid to phosphorus pentoxide to the C12-C18 alcohol is (1.3 to 1.3 to 1)-(1.1 to 1.1 to 1); and reacting the monoalkyl phosphate ester with a mixed alcohol of propyl alcohol or/and butyl alcohol, amyl alcohol, hexyl alcohol or/and capryl alcohol so as to obtain a dialkyl phosphate ester, wherein the molar ratio of the mixed alcohol to the monoalkyl phosphate ester is (4 to 1)-(2 to 1), and the mixed alcohol comprises 7-10% of propyl alcohol and/or butyl alcohol, 20-40% of amyl alcohol, and 50-60% of hexyl alcohol or/and capryl alcohol in percentage by mass. The phosphate gelling agent is good in flowability, suitable for continuous fracturing construction, and low in cost, and can, with short-carbon-chain alkanes, form an anhydrous fracturing fluid with a viscosity of 90-140 mPa.s.