A modified nano-silica gel for improving symptoms caused by bacteria and viruses and a preparation method and an application thereof. The patented nano-silica gel is modified by a modified compound to obtain a modified nano-silica gel to effectively reduce an amount of toxins excreted by sows, thereby providing piglets with a safe environment that is more suitable for survival. The modified nano-silica gel of the invention comprises: a nano-silica gel with a content of 13.0-92.3 wt %; a modified compound with a content of 0.15-3.50 wt %, the modified compound is an organic compound, a weight ratio of the nano-silica gel to the modified compound is 620:1 to 3.5:1; and water with a formula of H2O and a content of 7.5-86.8 wt %; the nano-silica gel, the modified compound and the water are stirred and mixed at a temperature of 40-80° C. to prepare the modified nano-silica gel.