The invention discloses a gelled electrolyte of a lead-acid storage battery and a preparation method thereof. The electrolyte comprises the following components: sulphuric acid, silicon dioxide, sodium sulfate, polyacrylamide, polyacrylate sodium, sodium molybdate, calcium molybdate, magnesium molybdate, sodium tungstate, potassium sulfate and deionized water; the method comprises the following steps of: adding the sodium sulfate into dilute sulphuric acid to obtain a dilute sulphuric acid mixed solution, then adding the dilute sulphuric acid mixed solution into a sodium silicate solution to obtain a silicon dioxide colloidal suspension, next firstly adding the sodium molybdate, the calcium molybdate, the magnesium molybdate and the sodium tungstate into a vapor-phase silicon dioxide nano-powder suspension to obtain a nano vapor-phase silicon dioxide powder suspension, then preparing a polyacrylamide solution and a polyacrylate sodium solution, then firstly uniformly mixing the silicon dioxide colloidal suspension and the nano vapor-phase silicon dioxide powder suspension, and then adding the polyacrylamide solution and the polyacrylate sodium solution into the mixed suspension to prepare the gelled electrolyte of the lead-acid storage battery. The gelled electrolyte of the lead-acid storage battery can be widely used in a storage battery with the capability of more than 20AH.