In this paper, the robust stability of cascaded two-port networked control system with disturbance in the plant, controller and two-port communication channel is studied. Cascading two-port connections occur when signals in a networked control system are transmitted over a series of two-port communication channels. Considering the distortion and interference occurring in communication, we consider $\mathcalH_\infty$ norm bounded disturbances in the two-port channel transmission matrix and gap disturbances in the plant and controller. The relationship between the robust stability of the closed-loop system and the networked control system is obtained based on the norm bounded communication channel perturbation, and a sufficient condition for the robust stability of the networked control system is given by means of geometric inequality. The numerical example shows the effectiveness of our conclusion.