The invention relates to a preparing method of modified emulsified asphalt, and belongs to the technical field of asphalt. A polyoxyethylene chain segment on polyethylene glycol is introduced into an epoxy molecular chain, and the modified emulsified asphalt containing a nonionic hydrophilic group is prepared and mixed with petroleum asphalt, modified basalt fiber and desulfurated rubber powder to prepare the modified emulsified asphalt high in cohesive force, high in high-temperature stability and excellent in elasticity recovering capacity. Due to the bridging action of the modified basalt fiber and desulfurated rubber powder in the petroleum asphalt, low-temperature cracking performance of the asphalt can be effectively promoted, and the mechanical property and shear strength of the asphalt are improved. The prepared modified emulsified asphalt is high in cohesive degree, low in temperature sensibility and good in abrasion resistance and has the advantages of being simple in process, high in environment adapting capacity and good in waterproof effect and achieving energy conservation and emission reduction and recycle resource utilization.