The invention discloses a plant-source pesticide of carya illinoinensis phylloxera notabilis pergande, and a preparation and application method thereof. According to a preparation method, fresh citron leaves and Chinese tallow leaves are grinded at a mass ratio of 1:1; extraction is carried out with an ethanol aqueous solution; and filtering is carried out so as to obtain a filtrate which is the plant-source pesticide. Citron leaves contain substances such as limonene and linalool, and Chinese tallow leaves contain substances such as flavones, phenols, terpenes, and coumarin; the above ingredients are capable of detoxifying and killing insects; operation of the preparation method is convenient; drug raw materials are widely available; cost is low; the raw materials are pure natural; the plant-source pesticide is friendly to the environment; no pollution is caused; and it is confirmed by practice that the plant-source pesticide is capable of preventing carya illinoinensis phylloxera notabilis pergande effectively.