The invention discloses a compound fertilizer capable of reducing cadmium lead content of vegetables in a slightly contaminated vegetable field and a preparation method thereof. The compound fertilizer is prepared from urea, ammonium chloride, ammonium nitrate, diammonium phosphate, a nitric phosphate potassium fertilizer, a calcium magnesium phosphate fertilizer, potassium chloride, sepiolite, kaolin, bentonite and power plant slag in a ratio. The preparation method for the compound fertilizer comprises the following steps of: A, preparing the sepiolite; B, preparing the kaolin; C, preparing the bentonite; D, preparing the power plant slag; and E, mixing the raw materials prepared in the steps A, B, C and D with the urea, the ammonium chloride, the ammonium nitrate, the diammonium phosphate, the nitric phosphate potassium fertilizer, the calcium magnesium phosphate fertilizer and the potassium chloride in the ratio, and performing production processing to prepare the compound fertilizer. The compound fertilizer is mainly characterized by comprising 36.5 to 43.5 percent of passivator which can effectively reduce active state cadmium lead content of soil and cadmium lead content of the vegetables, and 30 percent of nutrients of nitrogen, phosphorus and potassium, so that the active state cadmium and lead contents of the soil in the slightly contaminated vegetable field are reduced by 41.3 to 52.3 percent and 36.0 to 58.5 percent respectively, the cadmium content and the lead content of vegetable products are reduced by 30.1 to 52.8 percent and 27.9 to 51.0 percent respectively, and the compound fertilizer is suitable to be popularized and applied to many heavy metal contaminated areas.