Adding improver to improve the mechanical properties of powdery clay is one of the commonly used ways to improve the roadbed soil, in order to give full play to the advantages of a single polyvinyl alcohol, lignin fibre materials to improve the soil to complement their respective shortcomings, based on triaxial consolidation undrained shear test, the mechanical properties of polyvinyl alcohol-lignin fibre composites to improve powdery clay under the conditions of different mixing ratios to carry out experimental research to analyse the stress-strain curve characteristics and change rule of the improved soil. The mechanical properties of poly(vinyl alcohol)-lignin fibre composites to improve powdery clay under the conditions of different mixing ratios were investigated to analyse the characteristics of stress-strain curves, shear strength parameters and modulus of elasticity. The results of the study show that, compared with the composite improvement of polyvinyl alcohol-lignin fibre, the stress-strain curves under different circumferential pressures of single lignin fibre or polyvinyl alcohol improved pulverised clay soil show strain softening, and the angle of internal friction, cohesion and modulus of elasticity have a small increase compared with that of the plain clay soil. In the case of polyvinyl alcohol-lignin fibre composite amendment, the stress-strain curves under different circumferential pressures show strain hardening type, with better destructive toughness and higher preload value; the cohesion of the 3% polyvinyl alcohol and 1% lignin fibre composite amended soil was increased by 96.55% compared with the single amended and vegetative soils, the change in the angle of internal friction was not obvious, the compression was reduced, and the elastic modulus was increased by 71.23%, and the ability to resist external deformation was increased. The ability to resist external deformation increased. The best effect of the combined improvement was achieved when the polyvinyl alcohol was used.