Abstract: In this experiment, Chinese fir wood was treated by impregnation of phenolic resin and montmorillonite solution under positive and negative pressure imitating breathing environment. The effects of negative pressure, negative pressure time, positive pressure and positive pressure time on weight gain rate of Chinese fir wood were studied, and optimal progress was confirmed by orthogonal test. The density, weight gain rate, surface hardness, mechanical properties, dimensional stability and flame retardancy of the compacted modified Chinese fir wood were analyzed based on the impregnated Chinese fir wood with the optimal technology. The microstructure and functional groups of the modified Chinese fir wood were analyzed by scanning electron microscopy and infrared spectroscopy. The results indicates that the weight gain rate of wood is the best when negative pressure –0.095 MPa, negative pressure time 20 min, positive pressure 1.5 MPa and positive pressure time 1.5 h. Under this impregnation process, the density of Chinese fir after compression densification treatment increased from 0.328 g/cm³ to 0.784 g/cm³, and the static bending strength, elastic modulus and surface hardness increased by 34.7%, 38.4% and 85.6% respectively; the dimensional stability results showed that the water absorption and volume expansion of the modified fir are significantly reduced. The scanning electron microscope(SEM) showed that the modifier penetrates mainly through tracheids, ray cells and pits, and the pores inside the wood were well filled. The Fourier transform infrared spectrometer indicated that the free hydroxyl groups are reduced and the number of bonded hydroxyl groups and ether bonds are increased in the wood, where Si–O–C bonds are formed. The fire resistance test found that the modified wood has a good flame retardant effect.