Abstract: Biomass-based high-ortho phenolic resin fibers were prepared from eucalyptus bark, tree stem, and lignin. FT-IR, TG, DSC and mechanical properties as well as the measurement of free phenol, were used to evaluate the properties of different biomass-based thermoplastic phenolic resins. The influence of the amount of the same kind of biomass on phenolic resins, and the mixing process on mechanical properties of bio-based phenolic resins fiber were alse investigated. The results showed that the composition of lignin-based resin was uniform, the structure was stable, and the thermal stability was the best. The bio-based phenolic resins with three lignin ratios had similar ortho-position(O/P) ratios, and the ortho-position reaction ratios were all greater than the para-position. When the ratio of lignin and phenol was 1:4, the obtained resin had uniform composition and best performance. The internal mixing process could homogenize the resin and avoid overheating, which caused by internal heat generation. Combined with mechanical properties, the optimal conditions of mixing process of bio-based fibers were internal mixing for 15 min, rotation speed of 45 r/min, and internal mixing temperature of 135 ℃. The maximum strength was 168.6 MPa and the elongation at break was 2.1%.