The silica-magnesium gel impregnated modified Chinese fir has improved physical and mechanical properties. Exploring the fixing performance and mechanism of silica-magnesium gel in Chinese fir has significance for subsequent research and innovation. It is uses silica-magnesium gel as the modifying agent and fast-growing Chinese fir as the base material.Modified Chinese fir was prepared after dipping and drying. FTIR and XPS were used to analyze the chemical composition and combination of naturalChinese fir and modified Chinesefir and discussed the distribution of silica-magnesium gel in wood and the permeability of modified Chinese fir. The experimental results showed that the physical and mechanical properties of the modified Chinese fir impregnated with silica-magnesium gel hadbeen significantly improved, and the density was above 0.5 g·cm^-3, the compressive strength and bending strength were increased by 99.73% and 58.48% compared with the natural Chinese fir.The end surface hardness was increased from 3 659 to 5 843 N, and it reached the performance index of medium wood. The results of EDS proved that the medicament was well filled in the cell cavity of the fir, and the main elements such as Si, O, Na, Mg and the impregnating medicament silica-magnesium gel were consistent and evenly distributed. Layered XPS tests were performed on the Chinese fir before and after impregnation. The O/C of the modified Chinese fir increased, and the content of each element at different depths was very close. The silica-magnesium gel was evenly distributed in the Chinese firand had good permeability.After leaching, the Si element content changed little, while the sodium element decreased, which may be caused by the dissolution and loss of some sodium salts, and the element content changes at different depths tend to be consistent. The resistance of the modified Chinese fir compared with sodium silicate, the loss rate of silica-magnesium gel was reduced to 10.8% in 96 h, and the effect was good. The FTIR test results of modified Chinese fir, natural Chinese fir, sodium silicate solution and leachate showed that the sodium silicate solution had the effect of destroying and leaching out the lignin and hemicellulose of Chinese fir, improving the permeability of Chinese fir and making it easier to interact with the medicament forms a chemical bond. The XPS spectrogram analysis of C, O, and Si elements showed that C(1s) shifted to low binding energy after modification, and the properties were more stable. The O—H binding was greatly reduced, and the Si—O binding increased. The silica-magnesium gel can form a stable in Chinese fir with a Si—O—C chemical structure, and the agent can achieve high-efficiency fixation on the cell wall. The research results provide new ideas for the loss detection and fixation research of modified wood and provide certain theoretical support for the follow-up study of modified Chinese fir impregnated with silica-magnesium gel.