The invention relates to a salt-free low-alkali dyeing process for cellulosic fibers and belongs to the technical field of textile dyeing. The salt-free low-alkali dyeing process comprises the steps of modification treatment, water processing, dyeing and aftertreatment of the cellulosic fibers, wherein in the modification treatment of the cellulosic fibers, a micromolecule quaternary ammonium salt cationic modifier and a macromolecule quaternary ammonium salt cationic modifier are adopted for carrying out modification treatment on the cellulosic fibers. According to the salt-free low-alkali dyeing process, two specific modifiers are adopted, and the synergistic effect of the two modifiers is used cooperatively with the specific dyeing step, so that salt-free low-alkali dyeing of the cellulosic fibers is realized in the dyeing process, pollution is reduced and the cost is reduced; moreover, the process is simplified; difficulty is reduced; modifying and dyeing effects are good; and the salt-free low-alkali dyeing process is suitable for industrial mass production.