According to the characteristics of the Dewar for long linear HgCdTe IRFPA detector with the large volume,many kinds of parts and the deflated sources of the different materials,especially integrated with the inline pulse tube filled with the 3MPa high-pressure helium,based on the material analysis of gas diffusion and infiltration theory,the vacuum life estimation model for the long linear FPA Dewar assembly was established.The vacuum lives of the split-type and integrated long linear FPA Dewar were calculated and predicted values of the vacuum lives are both more than 2 years.The online monitoring structure for Dewar vacuum degree was designed to monitor the vacuum of these two types of Dewar for a long period of time.The predicted results were compared with the measured value,the relative error of split Dewar is 5.8% and the other is 6.96%.Because the integrated Dewar vacuum is difficult to estimate,so it’s thermal performance is verified by the tests of the cooling performance,and there is no obvious change in the thermal load of the integrated Dewar.