Vibration isolation devices are widely used in engineering, and the actual systems are mostly multi-vibration transmission path systems with attached structures such as pipelines and cables. Therefore, ignoring the analysis of the attached structures can not correctly evaluate the vibration isolation performance of the system. Aiming at the typical multi-transmission path system, this paper establishes a double-layer composite active-passive vibration isolation system model with additional springs, and analyzes the force transfer rate and energy transfer characteristics of the system in the case of a rigid foundation and an elastic beam foundation. The influence of the system parameters such as attachment stiffness, damping ratio, and foundation stiffness on the vibration isolation performance is discussed, and the influence of the active vibration control position on the vibration isolation performance of the system is analyzed. This paper provides a theoretical basis for the design of the composite active-passive vibration isolation system with attached structures.