With the development of state power data network（SPDnet）， the data information and control signal of the real-time secondary voltage control system are expected to be transmitted on the standard TCP/IP network in order to improve the flexibility and reliability of wide-area control systems. The transmission delays introduced by the network should be taken into consideration during the design of the network-based closed loop control system. According to the traditional principles of secondary voltage control， a mathematical model for network-based secondary voltage control is developed considering the network transmission delays. A novel type of secondary voltage controller based on multi-step observation and delay compensation is designed to ensure the favorable control performance and the control stability in the network environment. The simulation results of the New England 39-bus system illustrate the validity and effectiveness of the network-based control scheme proposed.