Abstract: The oil production rate of oil-based drill cuttings pyrolysis is low and the amount of harmful components in the oil produced by biomass pyrolysis is high. In order to explore whether the co-pyrolysis of the two can produce synergistic effects, a fixed-bed reactor was employed to investigate the effects of the main factors, including pyrolysis temperature, final temperature retention time, heating rate, nitrogen flow and mixing ratio, on the co-pyrolysis of oil-based drill cuttings and biomass. The results showed that the pyrolysis effect increased with the increase of the final temperature and the final temperature retention time, and decreased with the acceleration of the heating rate. The nitrogen flow had a minor effect on the pyrolysis process. The optimal pyrolysis process parameters were 350℃ of pyrolysis temperature, 60 min of final temperature retention time, 10℃/min of heating rate and 0.15 L/min of nitrogen flow. The co-pyrolysis resulted in favorable synergies. When the proportion of biomass or oil-based drill cuttings was 30%, the oil content of the pyrolysis residue was lower than the theoretical value by 21.71% and 17.64% respectively. Co-pyrolysis reduced the generation of harmful substances in the pyrolysis process of biomass and increased the liquid yield of oil-based drill cuttings. The harmful components in the biomass pyrolysis liquid products went up to 74.92%, which were significantly reduced by adding an appropriate amount of oil-based drill cuttings. When the ratio of oil-based drill cuttings to biomass is 7:3 and 8:2, the harmful components were reduced to 22.74% and 17.57%, respectively. The research determined that co-pyrolysis could reduce the formation of harmful substances and increase the yield of pyrolysis oil. It has promising applications in the treatment and resource utilization of oil-based drill cuttings and the development of biomass.