The invention provides an emulsion paraffin water repellent for a medium density fiber board, which is prepared by taking solid paraffin and water as main materials, lauryl sodium sulfate, SPAN-60 and monoglyceride as emulsifiers, peregal 0 and tween-80 as catalysts and polyvinylalcohol as a colloid protecting agent. The water repellent comprises the following components in portion by weight: 40 to 45 portions of paraffin, 45 to 50 portions of water, 1.0 to 1.5 portions of lauryl sodium sulfate, 1.5 to 2.5 portions of SPAN-60, 0.5 to 1.0 portion of monoglyceride, 0.5 to 1.0 portion of peregal 0, 1.0 to 1.5 portions of tween-80, and 0.1 to 0.5 portion of polyvinylalcohol. The water repellent is unnecessarily melted or dissolved by a solvent when used; in addition, the water repellent also has the advantages of even film forming, small granularity, good dispersibility, good storing stability, easy combination with water solutions or emulsions of other materials for use, safety, high efficiency, economy and convenience, and can meet the requirements of the water repellent on low paraffin consumption and good water resisting property in the fiber board industry.