A method for preparing silica modified by a silane coupling agent, characterized in that the steps are as follows: (a) Solation of the coupling agent: water is added into the organic solvent and the pH value is adjusted to below 6 by dripping an acid or over 8 by dripping an alkali, and then the coupling agent is added to obtain that the molar ratio of coupling agent with water will be at the range of 1:0.1 - 1:10000; after standing for 0.5 - 48 h, the solution becomes clear and transparent, which means the hydrolysis is completed, and the stabilized sol solution of the coupling agent is formed; (b) Dispersing of silica: silica is added into the sol solution of the coupling agent, the amount of precipitated silica being less than 10 g/ml, whereas that of fumed silica is less than 1 g/ml using g/ml as a unit, which is a mass to volume ratio of silica to the sol solution; wherein, after silica is added into the solution, a uniformly-dispersed turbid solution is obtained through fully dispersing silica into the coupling agent sol-solution by ultrasonic dispersion for over 1 h and 1 - 100 times under an ultrasonic frequency of over 20 kHz, the time for an ultrasonic dispersion process being 10 min-- 1 h, wherein after each ultrasonic dispersion is completed, the turbid solution is stirred to lower the temperature to room temperature, and then the next ultrasonic dispersion is performed; (c) Modification of silica by the coupling agent and post-processing: the dispersed turbid solution is stirred at room temperature and evaporated to a solution weight of 0.1%-50% of the primary weight, further heated at 50 - 80°C and stirred for 0.5 - 120 h, and then heated at 81 - 260°C for 0.5 - 48 h for the reaction, and finally, silica modified by the coupling agent is obtained after drying and crushing processes, wherein after above steps and, the temperature of the remaining steps is controlled to less than 50°C to avoid a self-polymerization of the coupling agent sol to induce a gelation, through which solid precipitates are formed. (a) Solation of the coupling agent: water is added into the organic solvent and the pH value is adjusted to below 6 by dripping an acid or over 8 by dripping an alkali, and then the coupling agent is added to obtain that the molar ratio of coupling agent with water will be at the range of 1:0.1 - 1:10000; after standing for 0.5 - 48 h, the solution becomes clear and transparent, which means the hydrolysis is completed, and the stabilized sol solution of the coupling agent is formed; (b) Dispersing of silica: silica is added into the sol solution of the coupling agent, the amount of precipitated silica being less than 10 g/ml, whereas that of fumed silica is less than 1 g/ml using g/ml as a unit, which is a mass to volume ratio of silica to the sol solution; wherein, after silica is added into the solution, a uniformly-dispersed turbid solution is obtained through fully dispersing silica into the coupling agent sol-solution by ultrasonic dispersion for over 1 h and 1 - 100 times under an ultrasonic frequency of over 20 kHz, the time for an ultrasonic dispersion process being 10 min-- 1 h, wherein after each ultrasonic dispersion is completed, the turbid solution is stirred to lower the temperature to room temperature, and then the next ultrasonic dispersion is performed; (c) Modification of silica by the coupling agent and post-processing: the dispersed turbid solution is stirred at room temperature and evaporated to a solution weight of 0.1%-50% of the primary weight, further heated at 50 - 80°C and stirred for 0.5 - 120 h, and then heated at 81 - 260°C for 0.5 - 48 h for the reaction, and finally, silica modified by the coupling agent is obtained after drying and crushing processes, wherein after above steps and, the temperature of the remaining steps is controlled to less than 50°C to avoid a self-polymerization of the coupling agent sol to induce a gelation, through which solid precipitates are formed.