The invention discloses a seed coating agent, which contains the bactericides fludioxonil and difenoconazole and the insecticide dinotefuran as the active components. Specifically, the bactericides fludioxonil and difenoconazole and the insecticide dinotefuran are in a mass ratio of 201:1-1:20, and the balance water. The seed coating agent prepared from the components is subjected to coating according to a drug-seed ratio of 1:2-1:1000, can achieve a very good control effect on earlier stage diseases and pests of wheat, obviously improves the seedling emergence rate, plant height, fresh weightand other indexes, is significantly better than conventional coating agents, is a good coating agent for wheat seeds, and also can be applied to coating of soybeans, corn, potatoes, rice and other crops' seeds and tubers. The coating agent has the characteristics of easily available raw materials, low cost and easy preparation.