The invention discloses a barium-strontium scale cleaning agent and a preparation method thereof. The barium-strontium scale-removing agent is prepared through a reaction of, by weight, 20-40 parts of a chelating agent, 20-30 parts of a surfactant, 10-15 parts of an auxiliary agent, 5-10 parts of sodium hydroxide, and 20-35 parts of deionized water. The preparation method is simple. According to the method, deionized water, the chelating agent and sodium hydroxide are added into a reaction flask and are heated and stirred under a temperature of 40-60 DEG C; the surfactant and the auxiliary agent are sequentially added, and the temperature is maintained; and the obtained product is naturally cooled to room temperature, such that the cleaning agent is obtained. The barium-strontium scale cleaning agent has the advantages of good scale-removing performance, low toxicity, good stability, and no corrosion. With the agent, barium sulfate and strontium sulfate scales can be effectively removed, such that the agent has an important practical significance to oil field productions. The preparation method is simple and feasible, and the raw materials have wide source and low cost. Therefore, the cleaning agent and the method have good market values.