Belonging to the technical field of lead acid batteries, the invention in particular relates to a lead acid battery repair liquid and a preparation method thereof, and solves the problems of incomplete battery repair, troublesome operation, poor effect, easy secondary pollution, long preparation period of battery repair liquid, low preparation efficiency and poor stability in the prior art. The lead acid battery repair liquid comprises the following raw materials by weight: 0.5-1 part of nano-carbon sol, 0.3-0.8 part of tin dioxide, 2-5 parts of potassium polyvinyl sulfate, 3-8 parts of sodiumpolystyrene sulfonate, 1-1.5 parts of a mixed metal salt, 3-4.5 parts of sodium alginate, 0.8-1.6 parts of an antioxidant, 35-50 parts of a sulfuric acid solution, and 60-90 parts of distilled water.The lead acid battery repair liquid obtained by the invention has the advantages of good stability, comprehensive repair, convenient use, quick effect and long service life, and the lead acid batterycapacity repair rate is up to 100%. Also the preparation method is simple, has the characteristics of simple and easily available raw materials, low preparation cost, and is worth popularizing.