The modified polymethylsiloxane was obtained with hydrolyzed and modified polymethylsiloxane under alkaline conditions.Then，the modified polymethylsiloxane was mixed with Lewis acid，proton base，strong acid and strong base in a certain ratio in methanol respectively，and stirred at room temperature for 30 minutes.The XPS spectrum exhibited that the electron binding energy of metal ions in Lewis acid shifted to high binding energy gradually，while the electron binding energy of oxygen atoms in modified polymethylsiloxane decreased in different degrees.The different amounts of modified polymethylsiloxane were added into Lewis acid，protic base，strong acid and strong base solutions with different pH values，and the changed pH values of the solutions were detected.The results demonstrated that the addition of modified organosilicon increased the pH values of different Lewis acid solutions and strong acid solutions，but the pH values of protic base and strong base solutions were decreased.It is concluded that the main chain of the modified polymethylsiloxane structure is composed of Si—O—Si bonds.The lone pair electrons of oxygen atoms in the silicon ether structure can reduce the activity of cations in the soil solution to different degrees and has significant Lewis base properties.Several free hydroxyl groups in the modified organosilicon can provide hydrogen protons，which have significant protic acid properties.The organic silicon compound fertilizer prepared by mixing modified organic silicon and common compound fertilizer in a certain proportion can regulate soil acidity and saline-alkali properties.