The invention discloses a method and a device for preparing semi-coke. The method comprises the following steps: under the condition of co-pyrolysis reaction, mixing hot liquefied residues with dry coal, and carrying out co-pyrolysis so as to obtain hot semi-coke and pyrolysis gas, wherein the liquefied residues are substances generated by direct liquefaction of coal, and the temperature of the co-pyrolysis is 450 to 650 DEG C. The method provided by the invention can reduce the content of powder coke generated in the process of preparing the semi-coke, thereby increasing long-period stable operation of a pyrolysis system; meanwhile, obtained coal gas and tar have high yield and good quality.