The invention discloses a root irrigation and fertilizer and pesticide application device and method. The device comprises an electric sprayer, a drip irrigation hard pipe, a drip irrigation hose, a three-way valve I, a three-way valve II and a plug. The device is convenient to install and use, the pesticide application place, time and frequency of the device are flexible and easy to control, theuse cost of the fertilizer and pesticide application device and the labor intensity of operators are effectively reduced, the pesticide use amount is easy to control, the pesticide uniformity is high,phytotoxicity is not likely to happen, and the pesticide utilization rate is high; and the method is suitable for small-area fields where one or more crops are planted and irrigated in a drip irrigation manner, for different crops and different growth stages of the crops, the pesticide (fertilizer) application amount is different, according to the requirements of the different crops and the different growth periods of the crops for large and medium elements such as nitrogen, phosphorus, potassium and calcium and the occurrence rule of diseases and insect pests, fertilizer or pesticide is fully and evenly mixed, underground drip irrigation of the crops is completed, and the yield and quality of the crops are improved.