Time delay control of structural vibration was investigated in terms of output feedback,i.e.,utilizing the measurable output to realize an active vibration control of the entire system.The differential equation of motion of the system was first transformed to a statespace model with timedelay control input.Then,a transformation with a linear term and an integral term was employed to transform the original timedelay system into a form without timedelays.Accordingly,the principle of output feedback was used to design a control law for the system in terms of a reasonable performance index.Finally,as an example,the dynamical responses of a threestory model under earthquake loadings was investigated by numerical calculation,where the value of the time delay is integer times the sampling period and the integration time step is chosen to be identical to the sampling period.The numerical results show that the time delay control algorithm by output feedback proposed is valid and practically applicable.