The precision measurement and control instruments of the testbed will be disturbed by the vibration equipment in the working process, which will affect its normal operation. Therefore, it is necessary to use the vibration isolation device for vibration protection. Taking the doublelayer vibration isolation device as the research object, a multimount and multidimensional flexible dynamic model is established by combining the finite element method and impedance synthesis approach. The effects of different instrument mass, system structure and isolator parameters on the vibration transmission characteristics of the vibration isolation device are analyzed. The results show that the designed doublelayer vibration isolation device can meet the application requirements. Increasing the thickness of the upper table and reducing the stiffness of the vibration isolator can significantly improve the vibration isolation efficiency.