Abstract: The compensated water in the vacuum cooling is helpful to reduce the water loss of the cooled products. The effects of packed rate and the compensated water before cooling on storage period of King oyster mushroom were investigated by experiments. The packed rate was 20%, 40% and 60% respectively. The compensated water was 0, 12 and 18 g/kg respectively. The initial temperature was 11℃ and 16℃ respectively. The results show that the pressure of boiling point will increase with the increasing of the packed rate, and precooling time of mushroom in the vacuum slot will prolong. The compensated water has little influence on the pressure of vacuum cooling, but has influences on water loss and precooling time of mushroom in the vacuum cooling process. After 14 days storage at 0℃, the mushrooms can keep good quality under the condition of 18g/kg compensated water and 20% packed rate.