The invention discloses a fosthiazate aqueous emulsion and a preparation method thereof. The fosthiazate aqueous emulsion comprises the following components by weight percent: 1-30% of fosthiazate, 2-40% of solvent and cosolvent, 2-8% of emulsifying agent, 1-5% of wetting agent, 0.5-2% of dispersant, 1-5% of stabilizing agent, 0-5% of antifreezing agent, and the balance of deionized water. The method comprises the following steps of: dissolving fosthiazate into the solvent, and adding the emulsifying agent, the wetting agent, the stabilizing agent and the dispersant to obtain an oil phase; and mixing the antifreezing agent and water to obtain a water phase, and gradually adding the oil phase into the water phase or gradually adding the water phase into the oil phase under a high shear condition, thus obtaining the fosthiazate aqueous emulsion. The fosthiazate aqueous emulsion disclosed by the invention has the characteristics of high efficiency, low toxicity, environmental friendliness, safety to human and livestock, and easiness for degradation.