The co-pyrolysis characteristics and the thermochemical transformation of organic carbon of oil shale mixed wheat straw biomass were investigated at different temperature stages (t=348, 476, 521 ℃) by the fixed bed product classification recovery. GC-MS was used to analyze the structure of pyrolysis products qualitatively and quantitatively. The results show that the synergistic effect is mainly reflected in the catalysis of minerals in the pyrolysis process of biomass in oil shale at t=348 ℃, and it is also reflected in the influence of minerals in biomass ash at t=476 ℃ on critical asphalt molecular cracking process. The H/C atomic ratio of biomass pyrolysis products is significantly increased by the mixed pyrolysis, and the transfer of oxygen elements from pyrolysis oil to pyrolysis gas is promoted to improve the production of shale oil and promote the early pyrolysis of long straight carbon chains. The heteratomic hydrocarbons generated at t=476 ℃ pyrolysis are also increased to a certain extent.