A handheld monitoring and early warning device for Fusarium head blight of in-field wheat includes an acquisition card, a processor, a camera, a touchscreen, a power supply, and a 4G network card. The acquisition card is configured to acquire data. The processor is configured to analyze the acquired data, to obtain the growth of wheat based on a deep learning algorithm. The camera is configured to acquire root, stem, and ear information of in-field wheat. The touchscreen is a medium configured to perform human-computer interaction. The power supply is configured to supply power to the monitoring and early warning device. The 4G network card is configured to perform data communication and at the same time communicate with an external cloud server. Further disclosed is an early warning method of a handheld monitoring and early warning device for Fusarium head blight of in-field wheat.