Aiming at the shortcomings of the traditional drying method of polyethylene terephthalate (PET) materials such as high energy consumption and low efficiency, the work aims to study the technology of deep drying of PET by microwave and develop the experimental device based on the characteristics of high speed, high efficiency and easy control of drying materials by microwave. The microwave frequency-tuning and variable power drying technology was proposed, and the microwave uniformity was improved by actively adjusting the frequency. Combined with microwave variable power technology, the temperature of PET material was controlled at 170-180 °C, the temperature uniformity of PET material was improved and the occurrence of "thermal runaway" was prevented. When the drying time was 2 h, the deep drying of PET was realized, the energy consumption rate was 1.03 kW.h/kg, and the moisture content was reduced to less than 0.01%, which met the requirements of subsequent injection molding processing of packaging materials. Microwave frequency-tuning and variable power technology is suitable for deep drying of PET materials, which has advantages over traditional drying methods in terms of time and energy consumption.