Factors resulting in vacuum failure are analyzed. The influence of leakage on the vacuum lifetime of a Dewar can be controlled strictly by using an ultrahigh sensitivity leakage detection technology. The outgassing decline characteristics in the vacuum jacket are described by using the outgassing model in the form of power i.e. q(t)=q₀(t/t₀)_-α. The vacuum decline process in the vacuum jacket of the Dewar can be accelerated by means of temperature. The influence of temperature on the outgassing rate of material is described by using the Arrhenius model q=q₀exp(-E/RT). The acceleration factor can be determined according to the results of theoretical analysis and outgassing experiment.