The co-pyrolysis characteristics and related synergistic mechanism of Shenmu bituminous coal and Huadian oil shale at different blending ratios were studied in TG analyzer and fixed bed reactor. The results showed that the experimental values of weight loss from co-pyrolysis was higher than the calculated one, indicating that the possible interaction during co-pyrolysis could promote the release of volatiles and suppress the char production. The synergistic effect between coal and oil shale increased the oil yields and decreased the yields of water and char, presenting as the obvious effect of increasing oil and decreasing water in co-pyrolysis of Shenmu coal and Huadian oil shale. When the mass ratio of Huadian oil shale to Shenmu coal was 1:1, the highest oil yield was obtained of 9.84% and increased by 8.8% comparing to the calculated oil yield. Co-pyrolysis contributed to the increase of light oil content and yield. When the mass ratio of Huadian oil shale to Shenmu coal was 1:4, the light oil content higher than 80%, and yield was about 7.5%, increased by 8% and 11.2% compared with the calculated values, respectively, demonstrating that addition of a small amount of oil shale can obviously improve the pyrolysis oil quality. The hydrogen-rich components and radicals from oil shale pyrolysis helped to inhibit the polymerization of aromatics produced by coal pyrolysis and facilitated the conversion of aromatics into oil products, thus increased the pyrolysis oil yield and quality.