The conceptions of generalized stability and priority judgment function of real-time node which guaranteed the generalized stability were put forward aiming at the problem of Networked Control System (NCS) real-time performance based on shared Ethernet. From the perspective of control theory and communication theory, generalized stability and priority judgment function were applied into Real-time ETHERnet (RETHER) by using real-time performance improving method of avoiding collision based on protocol in Ethernet communication protocol. Therefore, token was passed to the real-time node with highest priority and real-time data was sent, NCS real-time performance was improved. Finally, simulation results demonstrate the effectiveness of the proposed method.