Bio-oil is the only liquid carbon-containing renewable resource. Due to its complex composition, low calorific value, high acidity, high viscosity, and other factors, it requires upgrading before further utilization. Electrochemical upgrading is a novel, mild and easily controllable method for bio-oil improvement, but it still faces the challenge of coking caused by bio-oil polymerization, which reduces the quality and yield of upgraded bio-oil. By conducting electrochemical upgrading experiments on modulated bio-oils containing different concentrations of acetic acid and aromatic-rich fraction (ARF), and characterizing the solutions and coke after the electrochemical reactions, the effects of acetic acid and ARF on coke yield were investigated, and the influence of acetic acid and ARF on bio-oil polymerization coking was discussed. The results showed that acetic acid could inhibit bio-oil polymerization coking. Adding 1% mass fraction of acetic acid could reduce coke yield by about 25%, and the coke yield could be further reduced as the acetic acid concentration increased. The ARF could promote bio-oil polymerization coking. When the ARF′s mass fraction increased from 60% to 70%, the coke yield increased by about 70%. When the ARF′s mass fraction increased to 80%, the coke yield increased by about 150%. Acetic acid inhibited the self-condensation of phenolic substances in bio-oil, reducing the rate of polymerization coking reaction, while ARF enhanced the hydroxyaldehyde con densation reaction, increasing the rate of polymerization coking reaction.