Based on the theoretical analysis of the cantilever beam structure of the detector-dewar assembly , the optimal design method of the mechanical weak structure of the dewar assembly is proposed, and Ansys software is used to simulate the structure of the dewar assembly before and after optimization. The results show that the modal first order fundamental frequency of dewar assemblies is significantly increased, which is 130% higher than that of parallel supported assemblies and 317% higher than that of conventional unsupported assemblies. Through the test verification, it is found that the vibration resistance of dewar assemblies has also been greatly improved, and 15g durable random vibration, 176g short-term mass random vibration as well as 2000g mechanical impact can be resisted.