Abstract: Abstract: In order to reduce the energy consumption of freeze drying for fresh water-oat and to improve the quality of the finished lyophilized products, the tests of 3 different kinds of freeze drying, including hot-plate vacuum freeze drying, microwave vacuum freeze drying, hot-plate and microwave combined vacuum freeze drying, were launched with the assessment indicators of total energy consumption, and volume retention, rehydration rate and aberration for energy or quality results respectively. The study showed that the 35℃ hot-plate vacuum freeze drying could obtain high-quality finished products, but with too high energy consumption. The 60℃ hot-plate vacuum freeze drying or 3 kW microwave vacuum freeze drying could reduce energy consumption of lyophilization, but the quality of water-oat was impaired as well, because excessive moisture sublimation rate resulted in the more destruction of the microtexture in water-oat pieces. The method, which used 35℃ hot-plate vacuum freeze drying to dehydrate to a certain degree, and then used 60℃ hot-plate vacuum freeze drying or 3 kW microwave vacuum freeze drying, could effectively reduce energy consumption and obtain high-quality finished products at the same time. On this basis, the uniform design was used to carry out the test study on the optimization of process parameters of hot-plate and microwave combined vacuum freeze drying. In the test, hot-plate temperature, dehydration switching point and microwave power were considered as test factors, which were all divided into 13 levels. Besides, according to the actual work situation, the hot-plate temperature was from 30 to 60℃, the dehydration switching point was from 72% to 90%, and the microwave power was from 1.2 to 3 kW. According to the experimentally measured results, the stepwise regression analysis method was used to exclude the non-significant items, and then the quadratic regression equation of total energy consumption, volume retention ratio, rehydration rate and aberration for heating plate temperature, dehydration switching point and microwave power was obtained. The influence mechanism of 3 experimental factors to above-mentioned 4 investigation targets was analyzed by the dimensional slice equipotential line figure. The results showed that the total energy consumption, volume retention ratio, and rehydration rate decreased and the aberration value increased with the hot-plate temperature and microwave power increasing. On the other hand, the influence of dehydration switching point on total energy consumption, volume retention ratio, rehydration rate and aberration depended on the value of hot-plate temperature and microwave power. If the setting temperature of heating plate had greater influence on total energy consumption, volume retention ratio, rehydration rate and aberration than the setting power of microwave, the total energy consumption, volume retention ratio, and rehydration rate decreased and the aberration increased with the dehydration switching point increasing. And if the setting temperature of heating plate had less influence on total energy consumption, volume retention ratio, rehydration rate and aberration than the setting power of microwave, the total energy consumption, volume retention ratio, and rehydration rate increased and the aberration decreased when the dehydration switching point increased. At last, the comprehensively weighted grading method and the stepwise regression analysis were used to obtain the regression equation of comprehensive index with the heating plate temperature and dehydration switching point. Furthermore, the optimization results of freeze drying process parameters were obtained by the multivariate linear constraint optimization method, which showed that the hot-plate temperature was 30℃, the dehydration switching point was 72%, and the microwave power was 3 kW. Under the optimum condition, the comprehensive weighted evaluation value was 76.07; and the total energy consumption, volume retention ratio, rehydration rate, and aberration were 90.6 kW·h, 51.86%, 10.59 and 4.32, respectively.