The invention discloses a preparation method for cold recycled asphalt emulsifier. The preparation method comprises the following operation steps: 1, taking alkaline-process papermaking black liquid, adjusting a pH value of the alkaline-process papermaking black liquid and filtering out and removing insoluble substances; 2, adding hydramine into the alkaline-process papermaking black liquid and evenly dissolving; warming a reaction system to 40-60 DEG C, dropwise adding epoxy chloropropane and reacting for 2h-5h; 4, continuously heating up to 70 to 100 DEG C, and reacting for 2h to 7h; 5, adding unsaturated amine polyether into the reaction system and obtaining a target product after reaction. No papermaking waste liquid is utilized to extract lignin, a process of adding alkaline water to dissolving the lignin is avoided, a technology is simple and safe, equipment investment is small, and secondary pollution to the environment is avoided. The prepared emulsified asphalt has an excellent emulsifying effect by using hydramine and unsaturated amine polyether, and mixture has good work time, excellent early strength and excellent freeze thawing splitting strength. By means of the method of preparing cold recycled asphalt emulsifier, environmental pollution can be reduced.