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In a Jupiter exploration mission, the Jovian radiation belt has a strong radiation characteristic with high energy and large flux. Based on the data from the radiation test on device, the Jovian radiation belt model and solar proton model, we introduce a method to evaluate the failure possibility and the confidence level of the RDM (radiation design margin) caused by the total ionizing dose after shielding layers, which includes the radiation environment variability in the Jovian mission. Using this method, we can approach a balance among the device ability, shielding thickness, and failure probability. We find that the Weibull distribution fits the failure possibility of the TL084 experimental data well. For a mission in an equatorial orbit with an altitude of 10 radii of Jupiter, the proton flux of the radiation belt is 3 orders of magnitude larger than solar proton. When the shielding thickness increases and the duration of mission decreases, the failure probability of the TL084 caused by the total dose decreases. The mean lifetime of the TLD84 is shorter than 2 weeks after a 10 mm aluminum shielding. In addition, we calculate the failure rate of the TL084. When the shielding layer is thinned and the orbiting period increases, the device fails faster. When the RDM is set as 2, the confidence level after 1 mm aluminum shielding is about 89%. [ABSTRACT FROM AUTHOR]