Abstract: The effects of KCl-ZnCl₂ molten salt on the pyrolysis characteristics and pyrolysis products of heavy bio-oil at 400, 500 and 600℃ were studied. The results showed that molten salt increased the solid yield of heavy bio-oil pyrolysis and decreased the gas yield. Some compounds such as phenol, cresol, ethylphenol and 4-propylphenol had good enrichment effect, especially the relative concentration of cresol increased from 8.82% to 20.85% at 400℃, while the relative concentration of phenol increased from 2.18% to 8.62% at 600℃. During formation of char, molten salt reduced the content of carbon and increased the content of oxygen, increased the BET surface area and total pore volume of pores. Molten salt promoted formation of pore structure of the solid product and increased its average pore diameter.