The invention discloses an environmental-friendly warm mixed asphalt additive and a preparation method thereof. The warm mixed asphalt additive comprises the following components in percentage by mass: 0.1wt%-10wt% of fatty alcohol poly-oxyethylene ether sodium sulfate, 0.1wt%-15wt% of alcohol ether phosphate ester, 1wt%-15wt% of inorganic micro powder and 60-98.8wt% of water. The preparation method comprises the following contents: fatty alcohol poly-oxyethylene ether sodium sulfate, alcohol ether phosphate ester, inorganic micro powder and water are added into a reactor according to the proportion, continuously stirred for 0.5-2 hours at a constant temperature of 40-60 DEG C, then heated to 60-80 DEG C and continuously stirred for 0.5-2 hours to obtain the warm mixed asphalt additive. The warm mixed asphalt additive provided by the invention can effectively reduce the high-temperature viscosity of asphalt, and has the advantages of stable property, easiness in collection of raw materials, low production cost, simple and convenient preparation method, wide application range and the like.