The work aims to use sodium silicate (Na2SiO3) solution and polyethylene glycol (PEG) solution as modifiers to improve the mechanical properties, dimensional stability and thermal stability of fast-growing poplar wood and study the effect of sodium silicate concentration, polyethylene glycol concentration and molecular weight on the properties of modified poplar wood, and obtain the optimum impregnation process. The effect of sodium silicate concentration, polyethylene glycol concentration and polyethylene glycol molecular weight on the impregnation effect of modified poplar wood was investigated by single factor test. Sodium silicate/polyethylene glycol modified poplar wood and sodium silicate modified poplar wood were prepared by the optimum impregnation process, and their in-grain compressive strength, surface hardness, moisture absorption volume expansion rate and other properties and structural characteristics were measured to explore their differences with unmodified poplar wood. The results of single factor test showed that the modified poplar wood prepared with 10% Na2SiO3, PEG-400 and 5% PEG-400 had the best property. The grain compressive strength, bending strength, end hardness, diameter surface hardness and chord surface hardness of the modified wood were increased by 69.4%, 19.1%, 42.2%, 39.5% and 19.2%, respectively, and the hygroscopic volume expansion rate was decreased by 40.0% compared with the modified wood. After sodium silicate and polyethylene glycol modification, the mechanical strength and dimensional stability of fast-growing poplar wood are improved compared with sodium silicate modified poplar wood alone, so the sodium silicate/polyethylene glycol modified poplar wood has more advantages in property and application.