Abstract: Hickory (Carya cathayensis Sarg) is an endemic tree species in China, whose nut is worldwide famous for nutrition.The nut is rich in protein and oleic acid, linoleic acid and other unsaturated fatty acids.In addition, the nut has a variety of essential amino acids and mineral elements.Drying is an important but weak link in processing of walnut products.At present, drying method for the nut usually uses traditional hot air drying, which consumes high energy together with low drying efficiency and poor product quality.Microwave drying technology has the several advantages over the traditional method, which include high efficiency, energy saving, sanitation, high product quality and automatic control.It has been widely used in the drying processes of fruits and vegetables.Currently, most of nuts, such as macadamia nuts, cashew nut, Chinese chestnut and pistachio nuts, are dried by using constant power microwave.Although constant power microwave method is easy to operate and control, the treated nut is easy to be over-dried or burned.Furthermore, the uneven moisture diffusion and high speed of heat and mass transfer generated in the late stage of drying process of constant power microwave reduce the original nutrients and the sense quality.Recent researches have indicated that phased varying power microwave drying method can overcome these problems.In order to improve the?product quality, shorten the drying process and reduce drying energy consumption, the phased varying power microwave was used to dry hickory nuts.The technical parameters such as pre-microwave power, moisture content after pre-drying and later microwave power were optimized in this experiment.First, the appropriate range of the various factors of the microwave drying of the hickory nuts was determined by using the single factor experimental method.Then, by using the three-factor and five-level quadratic regression orthogonal experimental method, the relationships between the 3 factors and dehydration rate, energy consumption of drying process, protein retention rate, unsaturated fatty acid retention rate and overall score of sensory quality indicator of dried nuts were analyzed.The regression mathematical models based on experimental indices and factors were established and used to analyze the influence degree of 3 factors on drying process.Finally, the optimal process parameter combination was obtained for drying hickory nuts using the phased varying power microwave through multi-objective nonlinear optimization method.These combinations were as follows: pre-drying microwave power was 6.5 kW/kg, water content of conversion point was 23.4% (dry basis), and late drying microwave power was 3.3 kW/kg.By using these optimized conditions, dehydration rate was 4.072%/min, energy consumption was 3.467 kW·h/kg, protein retention rate was 92.15%, unsaturated fatty acid retention rate was 91.63% and overall score for sensory quality indicator was 35.28 for dried hickory nuts.Our results provide theoretical reference for drying production of hickory nuts.