This paper presents theoretical and experimental studies on robust control of a flexible plate with considering uncertain time delay.The varying extent of time delay considering in this paper is assumed to be known.the robust controller is designed based on a given delay in this varying extent.Firstly state equation of controlled modes of the system with time delay is obtained using modal function of cantilever plate.Then this state equation is discretized and transformed into a standard form without any explicit time delay by a particular augmenting for state variables.Finally robust controller may be designed based on the augmented system using H∞ control method.Effectiveness of the proposed treating method for uncertain time delay is investigated through numerical simulations and experiment.