The particle size distribution and Zeta potential of a kind of quaternary ammonium salts emulsified asphalt were investigated, and the effects of the amount of emulsifier and pH value on the storage stability were discussed.The results have shown that the amount of emulsifier and pH value had an obvious influence on the average particle size, Zeta potential and storage stability of the asphalt emulsion.Moreover, the experiment has shown that the optimum amount and pH value of the quaternary ammonium salt was 1.6 wt% and 4 respectively.