For a class of Multi-machine excitation system with transmission delays, an output feedback adaptive quantized control protocol based on k-filter observer has been proposed. Not all the states in Multi-machine excitation power system need to be measured, a class of k-filter observers is constructed to estimate the unmeasured state in the system, and to compensate the estimated error of the neural network approximator, the nonlinearity introduced by the quantizer and external disturbances. The traditional assumption of the upper bound of time-delay function is no longer needed. Instead, time-delay function approximator is used to deal with the influence of transmission delay between excitation systems. This kind of time-delay function approximator is composed of neural network. And according to the finite coverage lemma, it can approximate the unknown function with time delay only by entering a limited number of previous states. Moreover, by the initialization technique, arbitrary small L ∞ tracking error is achieved. Finally, the control signal is quantized by the quantizer and then transmitted to the communication cable, so that the Multi-machine excitation system is realized by computer. A group of experimental results show the effectiveness of the proposed control protocol.