A O/W type C-5 petroleum resin emulsion was prepared with paraffin wax as viscosity regulator and blend of nonionic emulsifier. Effect of HLB value and concentration of emulsifier on stability, droplet size, viscosity and surface tension of the petroleum resin emulsion were examined. The results showed that when the paraffin added with 30% percentage composition, the C-5 petroleum resin melt viscosity decreased obviously and the material in the low temperature mixing uniformly. The suitable HLB value is about 10.75 and emulsifier concentration is 16%. The orthogonal experiment results showed that optimum conditions were, emulsifying temperature 98℃, emulsifying time 20 minutes, stirring rate 5000 rpm and emulsifying water quantity 1/3. The O/W type C-5 petroleum resin emulsion which solid content is 40% was prepared under this condition; it showed excellent stability, small droplet size and low viscosity.