Abstract: Leakage and degassing rate is an important parameter to evaluate the performance of high vacuum multi-layer insulated dewar.Based on static pressurizing method,the leakage and degassing rate of a dewar of 210 L was measured.A profile showing the chamber vacuum level as a function of time was obtained,with a result of 2.0×10-8 Pa·m3/s which is only 1.0% of Chinese Standard that can satisfy the application requirement.According to the result,considering with the effect of environmental temperature,it is found that the insulation material and pre-treatment technology are the main reasons of high heat-insulating property of dewar.