PURPOSE: A Sophorae Radix root extract with an activity of preventing moth is provided to replace agricultural chemical and to prevent agricultural chemical-tolerant moth. CONSTITUTION: A method for preparing Sophorae Radix root extract for preventing moth comprises: a step of adding Sophorae Radix root to 5-15 times volume of ethanol and extracting in the dark for 40-60 hours; a step of filtering to collect extract; a step of concentrating the extract at 30-43C; and a step of freeze-drying the extract. A composition for preventing moth contains the Sophorae Radix root extract as an active ingredient. The composition further contains neem tree extract, derris extract or Melia azedarach L. var japonica Makino extracts. The Sophorae Radix root extract is used for preventing moth by diluting 5-15% of ethanol solution in 100-2,000 times of water and spraying.